Hello CiaranT,
I don't think anyone would be surprised to see them withdraw from the Irish market tbh.
As for who might buy their Irish mortgage book (which I am guessing, is very small...well, in mortgage book terms), perhaps the likes of Pepper, Dilosk ("ICS") or KBC perhaps.
Obviously, the quality of the loan book would influence whether it can be sold to another lender, or if it's more likely to be sold to a fund, but assuming it's in reasonable condition then I'd expect it could be sold quite easily given I imagine it to be quite small so would not cost a lot.
Obviously, there is also the potential scenario that they might retain the loan book and just run it down over time, appointing the likes of Capita or Pepper to manage it for them (although personally, I would anticipate a sale of the loan book myself).
I believe the Leeds mortgages were on tracker rates (albeit not anywhere near as cheap as other lenders once provided).
Those with mortgages from Leeds BS could do worse than explore the possibility of refinancing, as there may be opportunities to negotiate a discount with Leeds in the weeks and months ahead, if you are in a position to refinance.