With so much chaos in the Church, a woman can ask 10 different priest/bishops and get 10 different answers.
When I've seen this scenario, it has more to do with an unhappy marriage and a spouse trying to find a way out. He/she usually doesn't really have concerns that the marriage is invalid, but rather is wishing that it was! (Or, even more likely, they left / were left a long time ago and have now found a new person they'd like to marry.)
Some women in these circumstances choose to stay. Some women choose to leave. It is whatever God calls them to do and we can't fault either choice. God knows her heart.
Can you elaborate with an example? I can't think right now of a marriage impediment that a spouse thinks might exist that couldn't be resolved to ensure that you are indeed married. If you really think that your marriage might be invalid and decide not to pursue a declaration of nullity, wouldn't it make sense to resolve the doubt by instead re-affirming your marriage vows?
This raises another question for me. Say, for example, you think your marriage lacked true consent because it has become apparent that your spouse never intended to have children. Wouldn't it be sinful to ignore the situation and go on living like a married couple when your marriage was likely invalid?