Answer

It may make some sense, but it is really not compelling. There is a difference between a prohibition that I violate against another person and what another person does to himself. He can waive the pain, whereas I cannot waive it on his behalf. Beyond that, Tosafot’s view does not necessarily assume that the value of life is less than the value of honor, but rather that the prohibition of shaming is more severe than the value of life (especially once you subtract the flaw created in the shamer by the act of shaming).
But these words of Tosafot are, in my view, a nice homiletic idea, and they should not be relied on. What they say has some force only if one connects it to the well-known principle of the Binyan Tziyon regarding interpersonal prohibitions (like Rashi’s comments in Bava Kamma 60b about saving oneself through another person’s property). True, that does not seem to be Tosafot’s intent, but from there one can at least derive the halakhic conclusion that public shaming justifies self-sacrifice. But again, even according to that explanation, it is not because of the severity of the prohibition, but because of what I called “territory considerations,” and therefore there is no room for your a fortiori argument. It’s hard to elaborate here, and I assume you can find it by searching here on the site.