The rules in previous editions have made it pretty clear; you are stuck at .8 Essence forever. If you remove augmentation, you get an "essence hole". For example, my character has a R4 Used Skillwire system and an R4 Used Skilljack, totalling 1.0 Essence cost. When she eventually upgrades them to R5 Betaware, together they will only cost 0.7-- But she still only has 5 Essence. However, if she gets more 'ware, like, say, a Pain Editor that costs 0.3 Essence, it would "fill" the Essence Hole first, and wouldn't end up lowering my Essence by more.
Here's another example if that one was kinda scatted.
Buy R2 Muscle Replacement: 4 Essence
Sell R2 Muscle Replacement, buy R2 Muscle Toner & R2 Muscle Augmentation: 4 Essence with a 1.2 Essence Hole
Buy R1 Wired Reflexes on top of the Muscle Toner and Muscle Augmentation: 3.2 Essence
Essence doesn't come back, sadly. Related, this is why critters with Essence Drain (like Vampires) are so dangerous.