Of course there's no 'form of right', whatever that may be, be it SAHM, or SAHD. It is a mutual decision, and one that is constantly reviewable, in accordance with changing circumstances and needs within the familial and the individual contexts.
It shouldn't scare the absolute shit out of him to sit down and have a very clear and frank discussion, about the possibility of her returning to work, and what this means for everyone in the family. If he's always had a SAHM there, covering everything, and doing anything, it's highly likely that a vast amount of what gets done is invisible to him, and he needs to have full and accurate information. They need to decide what is most important for them as a couple, and yes, I do think it's very important that there are clear negotiations and agreements about who is going to do what, particularly in terms of housework, groceries, cooking, childcare, pick-ups and drop-offs, what happens if someone has to go away for work, sick days, holidays, parent teacher meetings, doctors appointments, all the wife work re Christmas and birthdays. . .
Or it's likely to be a very vague, 'oh yes love, I think it's best if you go back to work, the kids don't need someone at home now, I'm sure we'll muddle along, everyone else does, and you know I'll pitch in whenever I can. . .'