We've been assiduous in overpaying the 10% for the past umpteen years, so the capital we owe is very small but we're looking at about 15 years of interest payments. To be honest, other than notionally liking the idea of being mortgage-free, our monthly payment is, by London standards, laughably small (I know people paying significantly more for a small room in a shared house than we pay for a four-bedroom detached house with two garages, a large garden, bears, and a yeti-habited summer house). Don't credit our financial acumen, it was pure luck, we bought a house in an ungentrified part of zone 2 London at the right time, and we've gradually slid out of the capital into bigger houses without increasing (and even decreasing) our mortgage debt.
Our current ERP is quite high, generally it seems the more flexible the overpayment terms, the higher the ERP. Understandable, considering the market is built on the longer-term yield of mortgage products.
I presume when my wife's family pop their collective clogs we get their houses (and I imagine the taxes), there's some legal blurb that my wife keeps waving under my nose and I keep ignoring. I don't imagine I'll be seeing my parent's house, as ever, that'll end up with my sister.