"Reboot" is a rather nebulous term -- it can potentially refer to continuing a departed series with a sequel, expanding its universe with a prequel, or "remixing" the original series with new actors portraying the old characters (or archetypes of the old characters).

The latter was done really well by CBS's "Hawaii Five-0" remake from 2010 to 2020. But I'm in total agreement with you: I can't imagine ANYONE ELSE portraying Buffy, Willow, Spike, or the rest of the Scoobies. That's why I advocate AGAINST a remake -- and in favor of either a sequel or a prequel.