A unique vocalist is certainly hard to replace. When Sammy joined Van Halen it ruined the band in my opinion. Roth was an integral part of the sound.
There are many very talented cover or tribute bands out there. I’m OK with that because they don’t claim to be the original band. There is an amazing Thin Lizzy tribute band near me. No, they don’t have Phil Lynot or Gary Moore but they are very good. Plus I can see them up close for free.....
https://youtu.be/7ooN5bSVkOI
Much better in person.