From my POV it would have to allow you to keep access to high level content yeah. I can't see it working otherwise.
It's mostly a problem with how confusing the presentation is - what I conceptually envisage is a sort of "virtual" prestige level. Say your mining is 99, but you prestige. You're still 99 mining, but your virtual prestige level is now 1. If you mine some copper, which you can mine with your virtual prestige level, you get XP and virtual XP which raises your virtual prestige level. If you mine some iron, which you can mine normally (because you're 99) but not virtually (because you're 1) then you get regular XP, but not virtual XP, so your virtual prestige level can't rise.
That all makes sense mechanically, but I think it would be really confusing to display and interact with in practice. An alternative version which is a bit clunkier but easier to understand is that you can freely switch in and out of "prestige mode". So when you prestige your mining "becomes" 1. You level up to 17, but then you can switch off prestige and return to 99. When you next switch on prestige mode, you resume from 17 because the two are tracked separately. Something like that.
One of the biggest conceptual issues with prestige mode is that a lot of the game is about building up complementary bonuses from other sources. Anything which lets you keep access to existing unlocks and levels and things is going to lead to massive cross-skill benefits where you leverage your 99 in one skill to power level from 1 in another skill. Probably this is fine and would just be part of the meta, but I think a lot of players probably are imagining a more interesting journey than this.
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