Well it wont be behind hundreds, not yet anyway.
Regionals still have a separate Seniority list and their ability to bid for Jet Vacancies is within their list only... we haven't got a joint Seniority list.
If the company does start hiring externals, they can do so on a 1:9 ratio, being 1 external for every 9 regionals without any problems... this means 1:9 Pilots actually employed and appointed to Jet Courses.
However, if they can't meet the 1:9 Ratio we get into Tag and Release, which is where the problems occurred previously. For every External Pilot Hired (outside the 1:9 ratio), then 4 Regional Pilots get a reserved Jet Seniority number ahead of that External hire, they get "Tagged and Released" back to the Regionals. As we saw before COVID, that quickly added up to 100 or so Regional Pilots on reserved numbers and externals started pulling their applications and not fronting for interviews.
However, in raw numbers terms, there should be no reason to require externals in the next 12-24 months, certainly not above the 1:9 ratio as the Links are quite well stocked and the recent Jet Course plan is quite slow. If they are forced to turn externally because of Regional Pilots failing courses, this isn't a Regional specific problem... the problem is who they're hiring, not where they're coming from.