1) State delegations report their results, so only one delegate is required to be on the floor to report results.
2) States which fail to report their results are simply excluded from the required total. This has happened multiple times in the past.
3) Individual delegates report their vote to the state leader who then reports it to the convention - If the delegate or their alternative is not present and their vote not registered previously, the state leader may cast the vote as they see fit for the delegate.
So could ‘blue flu’ happen? Sure. Wouldn’t make a bit of difference.
If that registration is not bullet-proof, I would recommend state delegates for Trump sign a single, notarized statement of their vote and FedEx copies to their state leader, the RNC and the MSM. There seems to be good reason that all manner of surprises may occur at any level of this election cycle.