Will my credit score drop if I pay off the loan early?
No it SHOULDN'T affect your credit score if everything is settle with the lender. These are few things that might be harmful short selling (because the lender might take a loss), not paying remaining fees if any. Things to consider...how long it will take to find a buy for that neighborhood...but you can...

460K Loan on 575K Purchase
Yes very possible, give us a call...we've doing mortgage and mortgage only for more than 25 years, have a A+ rating with BBB. And we will glad to help get you that dream purchase...Lamin at Equity Mortgage Lending 1-800-949-1010 ext 2413.

HECM and reverse mortgage
it depends on why you are getting a loan, the closing cost maybe a little high. If you are getting it to do repairs or something relating to that you may want to get a HELOC, if you are getting it to pay of some high interest rate debt or something relating to that because or just supplement your retirement...