once time travel has come into play, surely all that matters is whether the magical technology in question will eventually be developed?

Not only do you need to have time travellers, you need to have time travellers who are interested in reviving you. The farther in the future you get the less the chance that any time travellers would want to revive you (although they might always want someone for historical interest so the chance might never go down to zero.) The more advanced the technology required, the longer it'll be and the less the chance they'll want to bother.

Perhaps you could go the cryonics-like route and have a foundation set up whose express purpose is to revive people some time in the future in exchange for payments now. While unlike cryonics there is no ongoing cost to keep you in a position where you can be saved, the cost to keep someone wanting to save you is still ongoing. This would still be subject to the same objections used for cryonics foundations. Of course, like cryonics, you can always hope that someone creates a friendly AI who wants to save as many people as it can.

There's also the possibility that some technology simply will not be developed. Perhaps there are some fundamental quantum limits that prevent getting an accurate remote scan of you. Perhaps civilization has a 50% chance of dying out before they invent the magical technology.