My insurer used drain specialist Augur
That says all you need to know... Classic upselling when insurance are paying, (most) of their no doubt rather large bill.
Looks to me like there's a Rubber Access point been fitted and possibly a section cut out the cast below, that has then been repaired with Denso tape. Whilst I would personally not be happy about having the repair internally, the rest bend is not 'displaced' it is merely a slightly smaller diameter that the cast.
Not sure how long you've been there, but if it's worked ok for a while, it may continue to work ok for a while more, replacing the rest bend may only move the reduction in diameter from the top of the bend to the bottom, and I know which end it would be better being at! Other, (possible and possibly cheaper), option would be to insert a 'Patch' into that section, which, (if done properly), would provide a more seamless run, and seal up any possible leaks between cast and clay bend.
I'd perhaps look to making a better job of the 'Denso' repair, (assuming that's what it is), if aesthetics aren't too important, get a Flexseal coupling, slit in lengthways, wrap it around the pipe with the slit at the back, and tighten the Jubilee Clips, this will provide a stronger, less likely to leak solution.
If appearances are important, then you'll have no option but to change the pipework sadly.