For some time now, UK companies selling "package holidays" (with hotel, air, etc. all from one vendor and with one bill) are required to put up funds that the government uses to repatriate those who are already traveling when a company goes under:
https://www.caa.co.uk/atol-protection/
Note that it does not cover trips that people put together themselves; in that case, I expect they'd only have to arrange for a flight home (as they paid for the other parts themselves).
The CAA (the UK's Civil Aviation Authority) already has a site up for Thomas Cook customers: