A court decision Tuesday forced the country's prime minister from office and disbanded the three top ruling coalition parties.
But they quickly were reconstituted under different guises and leaders met Wednesday to choose a caretaker prime minister.
A spokesman for the protest alliance, Parnthep Wonguapan, said protesters at Bangkok's international and domestic airports were ordered to "clean up and pack their belongings" before leaving the two sites Wednesday.
The first commercial airliner - a flight by the national airline Thai Airways from the resort island of Phuket - was scheduled to land at Suvarnabhumi international airport at 2 p.m. (0700 GMT), said airline spokeswoman Ajcharnaporn na Songhkla.
In what was billed as a hand-over ceremony, Vudhibhandhu Vichairatana, the chairman of the Airports of Thailand, hugged and shook hands with alliance leaders in front of a Buddhist shrine as protesters danced to folk music and trucks loaded with their gear rolled out of the airport.
"We want to clean up the airport before we leave. We want PAD (the alliance) to have a good image," said Bow Piyapat, a souvenir maker, as she wielded her mop around rows of check-in counters at Suvarnabhumi.
But the image of the alliance as well as Thailand in general has taken a bad battering, especially among some 300,000 travelers still stranded by last week's airport takeovers. The months of protests and political uncertainty is also hammering the economy and vital tourism industry.
At least six people have been killed and scores injured in clashes in recent months.
The protesters - who seek to eliminate the one-person, one-vote system - is also seeking to purge the nation of the influence of former Prime Minister Thaksin Shinawatra. They accuse Thaksin of massive corruption and seeking to undermine the country's revered constitutional monarch, King Bhumibol Adulyadej.
Thaksin was ousted by a September 2006 military coup, but the alliance alleges that governments voted into office since then have been proxies for the exiled Thaksin.
"The PAD will return if another (Thaksin) proxy government is formed or anyone tries to amend the constitution or the law to whitewash some politicians or to subdue the monarch's royal authority," one of the protest leaders, Sondhi Limthongkul, warned Tuesday night.
The country's Constitutional Court found Somchai's People's Power Party, the Machima Thipatai party and the Chart Thai party guilty of committing fraud in the December 2007 elections that brought the coalition to power.
"Dishonest political parties undermine Thailand's democratic system," said Constitutional Court President Chat Chalavorn.
The ruling sent Somchai, Thaksin's brother-in-law, and 59 executives of the three parties into political exile, barring them from politics for five years. Of the 59, 24 are lawmakers who will have to abandon their parliamentary seats.
"It is not a problem. I was not working for myself. Now I will be a full-time citizen," Somchai told reporters following the ruling.
Government spokeswoman Suparat Nakboonnam said Deputy Prime Minister Chaowarat Chandeerakul automatically took over Somchai's job pending selection of a caretaker prime minister. She said Parliament would have to endorse the pick within 30 days.
A meeting Wednesday among the three ousted parties, which vowed to stick together in a coalition, was being held in a northern Bangkok suburb and it was unclear when they would decide on the caretaker prime minister.
Somchai had become increasingly isolated in recent weeks.
Neither the army, a key player in Thai politics, nor King Bhumibol offered firm backing. Palace circles have not hidden their enmity toward Thaksin and his allies, rattling a decades-old consensus of absolute respect for the monarchy.
The alliance, often referred to by its acronym PAD, claims Thailand's rural majority - who gave landslide election victories to the Thaksin camp - is too poorly educated to responsibly choose their representatives and says they are susceptible to vote buying.
It wants the country to abandon the system of one-person, one-vote, and instead have a mixed system in which most representatives are chosen by profession and social group. They have not explained exactly how such a system would work or what would make it less susceptible to manipulation.
The alliance's rivals, government supporters who adore Thaksin for the generous social welfare policies his government implemented for the poor and rural majority when he was in power in 2001-2006, were angry, though uncertain what to do.
"People aren't going to just sit and watch another elected government toppled," said Pracha Niemjaroen, an electronics technician discussing politics with his friends at an open-air restaurant in the northern city of Chiang Mai.
Chaturon Chaisaeng, a former Thaksin Cabinet member, suggested there could be civil war if the protest alliance presses for a non-elected government.
"Why do we still condone the PAD, who are waging terrorist attacks against government buildings and the democratic system?" he said. "Do all Thai people have to bow to the PAD's orders and demands?"
Travelers were the clearest immediate beneficiaries of Tuesday's developments. Thai authorities had been running flights in and out of a naval air base at U-Tapao east of Bangkok, but its limited facilities left many travelers looking more like refugees than tourists.
