@Alec Norman lots of good advice in this thread. I tend to agree with @Lynn McGeeinthat if I were in your situation I would sell it (and no, I'm not just saying that because I'm a Realtor lol).
I remember when the market first crashed out here- my home was 40K upside down and we got transferred out of state. No biggie, I thought, the market will recover. It didn't. Two years later, my financial planner told me to sell it b/c it was 80K upside down. I resisted! After all, the market would bounce back and there's NO WAY I'm losing 80K! Well the market never did recover enough for that property and 9 years later it's 150K upside down. I've been told by two CPAs and even a JAG (military lawyer) to walk away from it. I won't (it's rented) because of my personal convictions, but this experience colors how I approach property now - even the ones I live in.
With that much profit to play around with, you could take the chance and see, as others have suggested, whether you like being a landlord. The biggest question I would ask, in this case, has already been asked: can you financially absorb the cost of that mortgage if the property is empty for 2 months between tenants. Will the profit you make be enough to overcome that hit to your bottom line?
If not, then even though this townhome could be worth double in 20 years, if I were in your position, I'd sell, take the 100K, and apply that to my future ("a bird in the hand...").