My 2p, and I am not BA, nor privy to the negotiations:
Covid19 is an unprecedented global situation. Now is NOT the time for the management to be taking advantage. Nor is it the time for infighting, settling old scores, or for crew to threaten strike action.
The most important thing is to get the wheels of the airline turning again, and this will require everyone's cooperation.
Could it not be agreed that as many BA staff as possible return to work under a "lifeboat" system of temporary reduced pay, part time rosters and skeleton Ts & Cs, (same for all, including management), on the express understanding by both sides that this will only be for, say, a year until green shoots start appearing. After this period, talks and negotiations will resume to restore pay and Ts & Cs and take the business forward, and nothing signed, accepted or implied now will be valid or enforceable after the "lifeboat" period.
Would that be feasible? It could get many back to work, earning at least something, with their ratings and SEP etc. current, and hopefully the business will survive.