I would say if you can reclaim the cost of the DADU in 2 years or less you can go for it.

In a flood situation the flooring could be reclaimed and used again.

"Reclaimed" wood is all the rage in furniture and decor right now.The diabetic strip thing has been discussed here before.  

It is VERY difficult to reclaim your property even if they were renting the house and you had nothing to do with it.

We served eviction papers- the resident was a no-show in court, so we got the eviction immediately.Then, we showed up with the sheriff to reclaim what was ours, and surprise!

Your goal at this juncture is to reclaim possession of your property with the least amount of damage. 4.  

How do I go about reclaiming this money?

I have two different break-lease options for people - they can break early with 2 months rent (one month plus the deposit, assuming there's no damage), and I will let them walk unconditionally - I reclaim utilities, yard care, etc.

Could this backfire on me if he chose to try and reclaim his right to the property during the original lease?

I surmise that 80% of the time renters never change the air filter and we find this is the point at which they start complaining of heat and ac issues; or high energy costs.Sometimes they remove the filter because they are too lazy to buy a new one; this can cause build up on the evaporator coil and eventually cause it to fail.This is not the primary reason for my visit, just the reason we chose a 3 months as a timeframe.During this visit I assess property condition, write down all repairs and send my guy out to fix them.I DO NOT offer the tenant the option to do the repairs themselves.Instead, I bill them and any money received goes to the repairs fist, rent second.I find this is a good way to set expectations with our new tenants and make sure they know we are serious about our properties.3 months before the lease ends we walk the property again.We assess the repairs needed and either they make the repairs or we do them.We again bill them the same way.This way, when the lease comes to an end they still care about their security deposit.They have not mentally written it off and left my asset trashed.I recommend you get in there and get the repairs started today instead of waiting for her to vacate.Now is the peak rental season and finding a tenant in the middle of winter will be problematic.Also, I generally sign 2yr leases, but if the lease ends in the winter months I shorten them to end during July.Offer cash for keys if need be, or offer to assist her in the move.Whatever it takes to reclaim this property I suggest you do it now before winter hits.It will be much less of a hassle.