Mahrez, Ndidi, and Kasper would be good signings for anyone.
Mahrez got his head turned and didn't get it back on straight until recently, if even that, but he still has the goods. Whether he could handle being under Jose is another issue, but I wouldn't mind signing him (after inquiring about other options, though).
Ndidi seems to be what LC was missing earlier in the season and has been a revelation. Good enough for United? Maybe, but I'd rather have Fabinho for DM. Again, a case of maybe if other options fall through.
Kasper is still in the top tier of PL keepers. If De Gea goes, can't go wrong with Kasper, but as above, after looking at other options (most notably Oblak & maybe Pickford).