If the guarantee never had to be exercised then the TK company pocketed the extra money.  

Is the point of the exercise the hypothetical, or are we actually talking about a $100k property?

But my dad who had gently nudged me into what at times felt like a ridiculous endeavor was also super conservative financially and convinced me to finance it on a 15 year loan.

Real estate can be good exercise though if you like house and yard work.

The best financial strategy for you is similar to the best exercise plan you can take.....it’s the one you can do consistently.

That deal we had also used an escalation clause to be sure to beat other offers in a multi-offer situation, but there weren't any to exercise the additional $2500. 

This may be an academic exercise but will give comfort on how deep in the water you are in extreme situations.

GENTLY WITH A CHAINSAW 

I bought it because I thought it would be a fun way to exercise.

Making extra payments became a simple and completely safe exercise because at any point I could bring myself back to even, so I made another extra payment without thinking about it too much, this time deliberately, and found myself two whole months ahead of schedule.