I have the identical concern, except mortgages here don't roll over into a default higher rate. You MUST requalify when your term is up. I have a variable rate 5 year renewable mortgage, (at 2.1%) and fixed rate 5 year mortgages (at 2.7%+) are also very common here. A few people may sign up for 7 or 10 year terms, but not many.
I FIRED this year, with my DH's income being only 25% of our previous total combined income. If rates rise at all, we will not qualify to refinance in 3 years, according to the rules.
YET, we have nearly 20 years left on the mortgage.
My solution --
1) If we keep to the same lender, it will likely roll into a new term without may refinancing questions. Not a problem if rates don't rise much in 3 years.. As time goes on, the mortgage gradually is paid off, and it is easier and easier to qualify for the smaller mortgages. DH's income may increase over time as well.
2) If we can't afford a very large mortgage based on FIRE income, I have available cash saved to pay down part of my mortgage, to the level we can be approved for. Alternatively, many banks will accept proof of invested cash in the retirement funds that cover the balance as a sign of credit worthiness. (may need to lock the investments in as collateral, however).
3) Last case, I am able to fully cover my mortgage with my own retirement funds. In Canada, you can hold your mortgage in your RRSP (retirement account). This means that I don't need to remove the cash (and pay income taxes) to pay off the mortgage, but can pay off the bank with the RRSP money, and create a "loan" or mortgage to myself that I continue to pay monthly.. to myself. This last option would be the equivalent of resetting my retirement allocations to be very heavily weighted to fixed income, rather than equities, and is a bit more pricey than a conventional mortgage, so it a last resort. But I will have full control over whether I approve myself or not. (LOL)
I was quite happy to know that there is ZERO chance of being kicked out of my home, no matter what the banks choose to say or do, despite having a very large resetting mortgage right now.
Does that help answer your question?
tldr: Essentially, have the money available in a retirement account to cover your mortgage if you need to. When you have money, borrowing money is much easier.