If they're willing to pay the £5m then it's fine atleast it's to Manchester United's benefit cause they can still sell him to another club then add what they sold him to the £5m they got from Chelsea and sign another player, Manchester United needs new players and majority of the funding would be coming from the sales of unwanted players so if Chelsea is ready to return back Sancho and pay the £5m then Manchester United should embrace it, well Sancho is a good player but I don't think his Career would work in England, we saw how well he excelled while in Germany playing for Dortmund maybe that's the most suitable league for him, maybe Dortmund might come to sign him permanently.
Sancho is good, but he's not PL quality. It's wrong for MU to hope other PL club to take him as a permanent transfer. The better they consider to send back him to the Bundesliga. I've heard dortmund still have interest on him. They can try that. Re-couping double digit million is far better instead of keep waiting his contract gets shorter.