ESA - LCWRA

Hello Just hoping someone could help me please. I was claiming New Style ESA which after an assessment I was put into the LCWRA group a while back. I am currently claiming UC and have entitled to PIP.
I am still technically employed even though it has been a long time since I have been able to work but my employer has kept me on their books and I haven't been getting paid anything from them for over a year, it more of a your jobs here when you're ready.
I know they cant leave this position open for me indefinitely so I really want to try and get back in some capacity.
I plan to go back and try a phased return with modified working. My main concern is failure and not being able to do it even though my head says I can. I'm worried that after all the stress of initially claiming ESA and UC and going through assessments etc that if I try work and fail after a few weeks that I am in a worse position than I was before I gave it a go and have to start the claims all over again.
What's the process if that was the case as Ive never been in this situation before? I really want to give going back to work a go but the back to square one if it fails is rally putting me off trying.
What would anyone advise please?

Thank you

Thanks Chris, I think it may be deemed full time hours even though i'm not actually going to work full hours initially as it may be a phased return to start and I would be paid as if working full time hours.
I called the ESA line and eventually got through and asked the question and was told that I would have to start a whole new claim and it wouldn't be with ESA as it is changing to UC and thats where the claim would have to go to. I thought that it sounded wrong so asked them to check if there was a fast track claim if I reclaimed within 12 weeks. They went away and came back and said I was right and as long as it is within 3 months I can renew my claim.
I don't have full confidence in the advisors knowledge so Im not 100% sure what to believe now