Usually I would expect that a call back to base will allow for the reserve iPads that are maintained and updated within your Flight Operations department, to be utilised to supply the required performance figures as a temporary mitigation measure.....until you can have the new replacement iPads dispatched to you.
As for the likelihood of two iPads failing at the same time....that's got to be a highly unlikely scenario aside from a possible corrupted database issue, and then your in a 'no go' situation IMHO until such time as the relevant EFB administrator has resolved the issues internally.
I would expect this to be dealt with as a matter of urgency, so hence it should be resolved as soon as feasibly possible - much like any TECH/AOG issue, it can happen and is subject to similar contingency plans.