I wouldn't worry too much about the waterpump, Yes if it fails completly there will be some engine damage, but its more likely start leaking before any complete failure.
You could say the same about the tensioner or the other idler pulley. But are you really considering replacing them as well??
Do the belt, inspect the waterpump for leaks or any bearing harshness and then dicide if its worth £100 extra.
I fitted a new idler when I rebuilt my engine and that new item failed after 150 miles!!!
Steve M
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Its all gone Norfolk!!!
Now in the Lotus position.