My experience with options and big tech organizations (worked for two of them) is that your granted options would continue to vest on the original schedule as long as (a) you're alive, and (b) still working for the company as an employee.
You would likely not get anywhere near the amount of additional options granted once you dropped down in org level. With the way you're thinking about it, that could be OK.
Once you leave the organization, you sometimes have a period of time after leaving where you can exercise vested options. Sometimes it ends on your last day of employment.
Whenever I was granted options, I was always given paperwork telling me what the vesting schedule and rules were. You could ask HR for a copy (they don't care one way or the other), or check and see if you have it yourself.
It seems like a reasonable plan as long as your org either has an office in Portugal or is willing to let you work remotely from there.