It's a very good idea to do what the manuals say.
Continue the flight as planned, but keeping a close eye on the pressurisation, and in particular - and far too few people know this - watching for correct functioning of the 5th/9th stage valve when thrust is reduced for descent.
From a practical point of view, prior to despatch you're able to uplift low level cruise fuel to address the FL250 cruise restriuction, but once airborne a decision to descend (unnecessarily) might well put you into a low fuel state to add to your other woes...
Last edited by Zorst; 18th Mar 2008 at 20:08.