I've more or less done exactly this. I left HK 6 months ago. My HK property worth $14m, a year ago my outstanding mortgage was around $3m, but I refinanced back up to 50% property value ($7m). It means I pocketed $4m to do what I want with (purchased a property in Australia). As a bonus, when I refinanced with Standard Chartered, they gave me 2.1% cash back on $7m. So a free $150k leaving present.
I didn't tell SC I was planning to leave HK. I did all this deliberately before leaving as I doubt they will ever lend to me again now that my income not in HK. But I've got a mortgage for 30 years with them, flat is rented out for more or less the same amount as my mortgage repayments, so it's pretty much self sufficient and I can sit back and relax. I havent even told SC I've left HK, just set my address as my office address, set all my mail preferences to email (but my coworkers in HK office still complaining the mail is piling up and I have to visit HK to collect it).