Thank you Dizz. From all my "research" so far I also have not come across the tongue flap option, so was a bit surprised when I heard that. Even more so when the doctor recommended that over the seemingly more common wrist flap option. Unfortunately, the doctor is very vague on how much speech impact there will be with this option, and we're out of time for 2nd opinions.

Maybe it is indeed because a relatively smaller part of the tongue is being removed and the wrist flap doesn't work well with the remnant tongue, not sure.

And thank you too for the info about what'd happen if there's no reconstruction. That's one option definitely off the table.