Cavity door broken

My lounge cavity doors have jammed. My husband has looked at it and said its the rail at the top has come away from its support beam within the wall. The only way he can fix it is tear part of the wall away. Hes been up in the roof and there is a beam on top of where the top rails are screwed so he cant acess it from above. HELP!!!!!!!!!!!!!!

I'd just cut out a square of plaster wall to repair broken door, then patch, sand and paint .. job done.

To return the square part I'd liquid nail a thin piece of timber on the inside across the hole .. let it dry .. liquid nail the plaster piece removed from the repair to the piece of timber - let it dry (making sure is all positioned correct).. Tidy up the edges and fill in the gaps with plaster fine filler.. a bit of sanding to smooth it all out .. and then all it needs is painting. But a professional may do it differently but thats how I've done to get access to the inner walls for plumbing and worked all fine.