Not sure I follow you there. If there's a blockage upstream of the HP pump the pressure in the line feeding into it is going to go from positive to negative pretty quickly (the pumps cavitated for some reason - not enough pressure being delivered to them is a reasonable inference).
Sorry, I thought you (or someone else) was saying that leaky seals were the root cause of the cavitation problem.... rather than a blockage downstream. Yes, I suppose air might get in through leaky seals with a vacuum in the lines.. but neither air nor vacuum are very good for running engines
