Its got leaves and green on the branches i'd say its certainly savable. I am sorry about your bout of bad luck, that's always tough. I am battling scale now on a few of my new trees and I know its gross and time consuming to get rid of. I am having pretty good luck with a mixture of Neem, Horticultural oil and Protekt sprayed on the trees once a week. I also take the time to physically remove any visible scale and then spray under them since they apparently lay their eggs underneath themselves. I also wash/rub away the sooty mold that develops. I only found a couple scale on the trees this week after spraying for the 3rd time/week in a row. I think I will be out of the woods after another spray or two.

I don't prune unless the branch is visibly dead/dried up brittle, if there is still green under the bark its alive and I would leave it. I would change out your potting mix, inspect the roots and trim back any dead/mushy ones, then after a few weeks start fertilizing it. I have a New Zealand Lemonade tree that completely defoliated and has come back with a great flush of new growth. I repotted from a soil mix to the 5-1-1 (you can search for it here if you don't already know whats in it) and started feeding it a very light dose of Foliage Pro and after a month and half I have lots of new leaves and two buds. I am up to the full dose of fertilizer now and it looks amazing. My Meyer lemon looks pretty sparse from overwintering and it hasn't flushed new leaf growth yet but I am hoping after I get it repotted this week that the new medium and the nicer weather will inspire more growth. My meyer is the most finicky of my trees and seems to like to drop its leaves over anything and everything. Hopefully more people will chime in and offer some good tips to kickstart growth. Good Luck!