BA is probably the most replaceable airline at LCY. They mainly duplicate other services. Scot Airways also cover the Edinburgh run (at much higher frequency), Lufthansa duplicate Frankfurt, and for Geneva Swiss already do the rest of Switzerland.
I don't think BA have had a lot of luck with LCY. Paris has gone, and the original Glasgow route was, as ever there, a real poor performer. I doubt they have ever made any money overall. Swiss would probably like to restart Geneva now, they were once very prominent at LCY, then went into a slide, now seem to be coming back.
There's one benefit BA have in yield from LCY compared to Heathrow, no connecting traffic at the low contribution BA allocate to it.
Edinburgh is maybe the only route worth having, but not worth keeping the RJs just for it. Maybe Scot Airways will buy them !