It has been suggested that FR might do a deal with VS, but now it looks unlikely, I doubt if DL is interested in VS operating LHR-DUB (and LHR-MAM/EDI/ABZ for that matter), when they operate direct flights to Dublin from ATL and JFK)
FR will not be doing a deal with anybody, the relevant competition bodies will decide and any deal to sell EI to FR will most likely include some form of ringfencing of LHR Slots. Assuming FR are given approval, seems most unlikely.
The BA-EI alliance has been weakening for the past 10 years at least
Not entirely true, the issues are quite recent. EI had added codesharing on BFS LHR before bmi deal was done. Leaving one world not a big issue between EI / BA. There relationship really only come under the spot light an appears strained since bmi purchase.
This will sort itself out in time. Too much at stake for both parties, particularly BA.