His hospitatisation is describes as precautionary, and if HMQ has gone to Ascot as usual, then I doubt there is any immediate cause for concern.
But, say he were to pop off suddenly, the monarch (as an institution) would be unaffected, but the Queen would obviously be mourning. That may lead her to decide to reduce activities, but I doubt she'd do a Queen Victoria. Indeed, carrying on might be her choice.
There is however recent precedent on what happens if a monarch cannot deliver the Speech. When George VI was too unwell to attend, the speech was delivered on his behalf by the Lord Chancellor.