If I am unable to do a workout on a scheduled day, I delay the workout until the following day and stay on the same schedule.
At this time of year, I have three scheduled "weight" workouts and four scheduled "event" or "met-con" workouts. I alternate days. If I miss a day of either, I resume where I left off.
I'm liking that very much these days. It's working well. Plus the staggered programming is really leading to some true strength and event performance gains I didn't think was possible at my age.
All the best,
Lifting heavy stuff is fun and relative......