Mini one new engine or not

Hi I recently bought a mini one as spares or repairs. It has 152 miles on it but in ok condition except the previous owner smashed the sump on a road hump, broke bottom engine mount and ran engine without oil until it stopped.

I have removed sump and there are a couple of 1 cm bits of metal in it. The engine is not however seized. Am I right to assume it’s knackered ?

if so is an engine swap very difficult for a bit more than a novice skill level ?

same question for stripping the existing engine and replacing worn parts ?

Any advice on buying a used engine off eBay ?

thanks.