I'd say the union will be vehemently against a salary drop for existing atcos.
A freeze (which is a real terms drop) is more likely but I think they'd struggle since they are still shovelling out dividends.
That's all for existing staff. Who knows what the terms might be for new starters, atcos do not have a very good history in not shafting new starters (see pensions etc)
With current pressures, I would suggest anyone not at the college already has a very good back up in mind for the foreseeable future. It is quite possible that the last route to a free ATCO license may be about to close