Yes, and I have done that before when a PM had not been active for years. I posted this in WikiTree Tech seeking a prophylactic solution for the future. When the PM approved the merge, she the likely thought that her involvement was complete and the merge would occur.
I believe that in the merge approval process, there should be explanatory language if one of the two profiles is not open, what needs to happen. Option one - notice that approval of the merge by the non-open profile will upon the merge with the open profile will result with an open profile. Option two - for an approval of merge of a non-open profile with an open profile, there should be a box to check to open the non-open profile as a condition of approving the merge.
Coding should be able to substantially resolve this from happening.