So for some reason I thought I’d check the cassette as the rear wheel has a very small amount of play.(bearings fine, everything tight any other ideas) and stripped it. Replaced with an old xt one.

Will I die?

Generally different ones depending on whether you have a 12T or 11T smallest sprocket (otherwise the chain may foul on the lockring rather than sitting ‘in’ the teeth).

think there both 11t cassettes although one is sunrace and the other xt. the xt one seems smaller od though.