Apart from the question of how to help Flybe without IAG and Easyjet complaining, the Govt has a much bigger problem to deal with right now
Assuming doctors / scientists are correct - the economy is likely to take a tumble later this year, which means less tax revenue for the Chancellor. There will undoubtedly be significant extra costs for HMG (eg around healthcare), meaning even less wiggle room on Budget Day.
There is a possibility maintaining public order will require paying police/army lots of extra cash. The NHS will seemingly be hiring lots of recently retired staff, all of whom will expect wages in return for work. Saving Flybe is insignificant in comparison.
If, as I expect, Flybe has seen a decline in forward bookings over the last 2 weeks, the owners will be aware how costly it can be to run an airline that flies fresh air around the UK
Maybe the Chancellor will find a magical money tree, but I would not be surprised if Flybe has chosen a bad time to be hoping for cash and ends up as collateral damage of the coronavirus episode