You could try cutting off the muffler level with the tailpipe socket, then cutting down the splits with a hacksaw - this will enable you to pry most of the stuck bit inwards and release it - it's the sealant that holds it solid, which hopefully won't go right to the end of the pipe.

I got a genuine Volvo replacement - the new tailpipe socket had so much clearance I couldn't get it to grip the muffler outlet effectively, and re-used the old one anyway!