Yes, you will get lifetime access and updates. But how much is “lifetime”?. Behind each item/theme are humans and if some author decide not to sell/update his items any more - he can remove that item from the market.
ok, so basically Envato gives lifetime access to download the update. then after it depends on the author’s mind if they want to keep their item on Envato or not.
Yep, Envato is “just a marketplace” and the authors are the owner of their items and they can do what they want with them - will they (and how much long) sell them and/or provide the updates.
And I must to add, it is not just about their “mind” - we are just humans and who knows what life can bring us (especially in this current times).