Peter,
I don't see the light at the end of the tunnel on this one. I could be wrong and I'd love to hear another perspective.
Can you acquire a home if the owner has filed for Chapter 13? It's possible but you can't hide from the courts. When title is pulled the pending litigation will be discovered and there won't be a transfer of ownership until it's approved by the court, administrator, etc.
Does it matter if the property becomes a short sale? This implies the owner will sell the property for less than the mortgage balance. This would be a good time to step in to try to buy the property outright if the price is right. If you were "subject to" in this scenario, well it would be awkward. Did you record your interest at the courthouse?
"Would the only reason a bank may call the loan due is if the property potentially can sell on a short sale for more than what’s owed on the principal?" OK, there's a contradiction in your question but I think I understand. The lender is going to call the note due if the owner falls behind on the payments. The 'rules' are spelled out in the mortgage but they usually try to work with a borrower that seems to earnestly want to catch up on payments and has the means. They don't only foreclose when they can recapture the balance of the mortgage. Often the lender takes a financial loss too.