Is it more economical than removing old tub and replacing with new?

I understand an AC or a roof has a life span and they will eventually need to be replaced but lets assume after 15 years of holding the property, nothing broke or wore out.What are peoples experiences with this?

I've told the tenant that the potential replacement has to be approved by me and if so, then we can take the next steps.

Check out Zillow or trulia if you don't have access to mls and look at recent sales. ignore valuations like zillows , zestimate  the actual sales in the area will give you a feel for the market but it does not replace visiting and walking the neighborhood and talking to the neighbors.

Based on the audience to whom you are speaking that seems like it would take one problem (your default) and replace it with another (a defaulted underlying loan).  

As it turns out the smoke and soot damage was fairly extensive, involving removing and cleaning tenants belongings, removing and replacing drywall in 2 bedrooms and a loft and removing and replacing insulation.

HVAC was replaced in the last 1-2 years.

I have not done any wholesaling or flips, but have replaced a roof and am finishing the complete rehab of the exterior on one of the properties as we speak.  

If they haven't paid their taxes in years, what else haven't they paid/replaced.

Have a nice slush fund ready to replace broken windows or nasty beer/puke stained carpet.