Note that those relationships are generally getting formalised as PSF in-kind sponsorships, so that they're not completely dependent on personal relationships with folks that work there, and so there's likely to be some prior warning if credits are being withdrawn and the Infrastructure team needs to make alternate service hosting arrangements (see https://www.python.org/psf/sponsorship/sponsors/ - while that listing doesn't separate out cash sponsorships from in-kind service donations, it's possible to make a reasonably informed guess as to which is which).

FWIW, switching from a hybrid Travis/Appveyor setup to a hybrid Travis/VSTS setup seems like it would be a reasonable way to go to me, since we have existing sponsorship arrangements in place with both MS and Travis CI, but no formal relationship with the Appveyor folks that I'm aware of (I believe we're just using their regular free tier).

Cheers,

Nick.