I'm one that will state that I believe, honestly, that Harry and Meghan deserve the break that they're taking now for 6 weeks. This is a couple that jumped feet first into full time royal work right after their wedding, made serious inroads into specific roles and had their first child. I see this hiatus as a delayed "adjustment period".
With everything that is going on with legal cases, a new foundation and perhaps the wish to have a larger family, laying low and relaxing and just enjoying family time for a short while, they'll be regrouped, energized and refreshed to handle whatever 2020 throws at them.
I'm sure they're keeping in close contact with Sandringham and keeping tabs on Philip's health issues and if they're needed, they'll be there. I'm hoping not though and all holiday plans go on as they've been planned.