I typed a response earlier quickly, while traveling. But I had some follow up questions.
Is your Fiance responsible at all for helping make your MIL’s final arrangements? Did she have a plan in place, burial plots, or directives for when she passed? For me, the day of the funeral was hard, but the days immediately after were extraordinarily difficult. So the post-funeral days would be *my* preference. I really like your plan of flying out to get things started with your work obligations, and then flying home for the funeral and staying home after to work and troubleshoot your replacement’s needs. In my experience, the immediate aftermath between death and funeral feels like a whirlwind and you feel like you are in shock and go on ‘autopilot.’ Something to consider, though, is whether or not your Fiance as her son has funeral related duties leading up to the burial.
If your Fiance has to do things like select coffins, sign contracts, create posters and compile digital photos for viewings, greet guests at a viewing prior to the funeral, the “leading up to” the pre-funeral days might be harder for him. I’m not sure if viewings are something that the family would be planning, but those are hard hours, too. It sounds like that planning is taken care of by someone other than your Fiance, though.
Would you be able to carefully navigate a second conversation with him expressing the decision you made by saying something along the lines of, “I will be flying out for work, but only for a few days. I was planning to go during time “y” (y being whichever you feel is the best balance – “during the pre-funeral arrangements” or “during the period immediately after the funeral for a few days to make sure things are handled at work”), ‘would you prefer I be here during period x, instead?”
I think making a decision FOR him verbally is a good idea when you two discuss the topic again, so that you can potentially read his reactions or trigger feedback from him. As long as it is followed with, “would you like me to do __ instead?” It will help him pretend everything is status quo if he wants to. And, by phrasing the conversation as a decision (“I decided to do x, would you prefer y?”) he might be able to give you a little feedback when you give him the opportunity to realize that something about that plan feels bad, or that everything is ok and that he doesn’t need you at that time *yet.*
My DH is facing his grandparent’s passing, soon, and I have been struggling with understanding just how will be best to support him. I have experienced several very close, painful losses but this will be the first, for him. So I empathize with your inner conflict. Hopefully, you will grow closer together through supporting him during this difficult time. Since you work in the nonprofit sector, I’m sure you have a big heart. It can be hard when that heart is pulled in so many directions, and you have a strong work ethic to make your decisions harder.