[I'm going to use the current Brexit example, but my question extends to other similar circumstances]
Certain situation require a bill be made into law in a timely manner, as with the blocking of no deal Brexit (if it isn't blocked before the current deadline for Brexit, the bill becomes pointless). My current understanding of royal assent is that the sovereign either in person or via commissioners of the crown must give royal assent, basically an OK, I allow this, before any bill can come into force as law.
Given the above I can think of a few possible scenarios whereby the sovereign is still compos mentis but due to some situation or another is unable to give royal assent in a short time span. As a simple example, imagine extremely poor weather causing a communication outage - this could easily delay royal assent for a day. There are as many others as you can imagine, but that's not the point of this question. Given a situation where the sovereign is still compos mentis, and is not intentionally delaying the process is there a contingency plan for a bill becoming law?