Sorry, didn't mean once wasm is in Chrome; it's already in Chrome. Meant once wasm is officially in Go. That version (1.11) is due to be released soon.
If you can quantify the amount of time & expense between the two, you get your answer:
1) no rewrite but painful updates over x period of time (total)
2) painful rewrite but easy updates over x period of time (total)
If the delta is small between the two, then think about how long you intend x period of time to be - when does it make financial sense?
Also, be aware that painful update experience winds up costing you in developer turnover. This can be a HUGE cost.
Short term thinking of "it's too painful to do a rewrite" has killed more companies than I care to remember.
But you need to figure out how to glean realistic and correct numbers for these things to justify EITHER decision. Neither option is always right - and if someone is saying it is, that person needs to be jettisoned ASAP- they're poisoning your well of information.
Go is the new darling child, and once wasm is in Chrome, it's going to get very big, very fast. And if they manage to polyfill to regular js (assuming that's still the plan - I haven't kept up), that's the end game maneuver.
For front-end, well, TypeScript 3.0 just came out...
Start looking for something elsewhere, but stick around until you either find something better and/or know what's what where you're at. There's nothing wrong with looking in the meantime.