Who could step in? Could be anything with a 50 seater or less, doubt it would be anything bigger, and not necessarily anyone currently operating from the UK
So, obvious options would be:
BMI Regional (to STN?)
Eastern (to STN?)
Aer Arann/EIR (probably to SEN)
Loganair (LTN/STN)
Blue Islands (LTN/STN)
Cityjet to LCY, if they have a spare F50. They might fancy the guaranteed income and think they've done PSO in Ireland
Otherwise, anything anyone can think of with that size aircraft
Minoan/Denim/Darwin etc