My question; Is the lien holder protected if I let the property be sold at the tax auction?

That is SUPER important if you are the note holder.

@Francis Dinh it is possible the lien holder will negotiate.

Your state landlord regulations will usually cover death of a tenant however in this case the son is the lease holder not the mother, and as such nothing has changed for you or him.

I've heard talk of possibly being a lien holder and basically have them pay me rent which would just go to the mortgage.

Use a reverse exchange where the 1031 intermediary purchases the new property and holds it for you in a special entity called the Exchange accommodating title holder. 

The reason being is that a foreclosure is not a foreclosure until its officially foreclosed and the property goes back to the lien holder.

Bucket with canvas tool holder liner w/ compartments for hand toolsTape measurePhone: for photo's of measurements of or any type of object weather a plumbing part or screw. and to use  as last resort to call someone else to help :)

Now the loan language is pretty strong stating that no assignment or assumption of the loan may occur without permission from the lien holder.You taking on a 2nd lien holder position this close to trustee sale just means that when the 1st forecloses, your lien falls off, so you just discovered the quickest way to lose $19K.

It comes down to debits and credits for the most part but there is also the logistical and sometimes conflicting component of investor requirements and 3rd party requirements (MI company, junior lien holder, senior lien holder, GSE, etc.) that at the least, influence the transaction or, can control the transaction beyond the seller's or lender's objectives outright.