With the belt off, replacing the tensioner takes moments. Even spinning it may not show if it is soon to fail. Space is at a premium, with the engine mounting in the way being removed for access, once in there, replacing all potential issues makes sense. "A stitch in time..."
I recently changed my belt and tensioner. The water pump spun fine and did not appear to be leaking. Fiat used a fair amount of sealant, so getting it off was hard work, I twice considered leaving it there. I did take it off, and there was evidence of slight leakage, so needed replacing. This is a 06 plate, with about 40k on the clock.
Your engine, like mine will not have timing marks, needing the tools to hold the crank and camshaft. Any garage without these should be able to borrow them from their cambelt supplier.
Of course, with the pump out, it adds the cost of new coolant, but that is a regular replacement item anyway. To avoid bigger bills and inconvenience later, do the whole job now.