I mean, this is basically the evidence standard that we use for flu/respiratory illness deaths, along with lots of other hard to measure interventions.
Personally, even if there were no deaths due to USAID being removed, it would still have been a strategically bad thing for the US government to do, in terms of soft power.
Additionally, the US are noted in development circles for circular aid, in that they gave a lot, but then required it all to be spent on US goods, so it was more of a subsidy for domestic producers.
I do agree that lots of people just jump on these numbers uncritically, because of prior beliefs about Musk/Trump/DOGE, but it would be very very surprising if there weren't lots of avoidable deaths due to the cutting off of aid. Like, the same thing could have been accomplished in a much better way by tapering off the aid as programmes expired.