I haven't encountered this scenario yet, but I would just substitute with running, stationary bike, etc. The whole point of rowing is to minimize impact and encourage consistency day-to-day. If we need to deviate on rare occasions to stay on track, it's not a big deal.

Not overthinking the exercise is a big part of not falling off the wagon. If you wrap yourself around that post it can really discourage you. Perfect is the enemy of really, really good things.