It's funny. I bought a new starter bendix just the other day and I noticed, when I took out the bolt holding the spring to the gear, that they've eliminated that fragile part, and instead, have a longer, one piece that extends all the way to the slotted drive part just aft of the intermediate bearing.
Over the years, I've had break, several of those weak bits and frankly, I couldn't see why they put them in, as theres no lateral flexing of the bendix when it engages, just twisting. So to see someone's eliminated it is good. Although, I don't know who the manufacturer was, because there was no brand name on the box, just 'Starter Drive Unit'.
Back to your question, No, it won't last if welded. I tried that once and it just broke up after a couple of starts. New units are relatively cheap.
"The trouble with the world is that the stupid are cocksure and the intelligent are full of doubt"..Bertrand Russell