The replenishment nerf will probably end up better for locks compared to everyone else since the mana proc from ISL will be much more valuable

Yes, Replenishment is applied to the 10 raid members with the lowest % mana. But it's unusual not to at least have a second source of replenishment in a 25 due to the population of Ret paladins and Survival hunters. Or even Shadow priests or another Destruction warlock. If you have a stable raid group and there is another source, you can count on it, though it's not a major source of mana anyways.

Sorry for the lack of updates to the OP. However raiding is now slow and I've gained some more motivation to re-write it so it should be up in a few days if everything goes well. I'm about halfway done as of now.

Are people honestly finding that they are getting the most out of ISL? Every encounter in Ulduar requires movement of some kind and as such you can simply time your lifetaps when you're running. (Unless you're lucky with RNG on Kologarn). It's so far away from a stand and nuke instance that I'm getting really quite sick of people worshiping ISL.If you can drop enough gear to get to 10% hit or so it's not necessarily the best idea to stack hit so that you can go for ISL. I would even go so far as to say that you shouldn't unless your raid needs the replenishment.

The idea that the choice comes down to a stand and nuke fight vs. lifetap-on-the-run doesn't take actual fight mechanics into account in my view. Those who say they just "tap on the run" rarely mention the raid dmg they may be taking that is often causing the movement. For example:
- XT Hardmode: If I’m running, half the time its because I have light bomb. This is an exceptionally poor time to life tap. I can also not tap during or in the 5-10 seconds before a tympanic tantrum
- Freya: Depends on the add phase. On hardmode there is no way I’m going to life tap when we’re downing the little flowers. I’d also be very careful during the spirit phase because of the charge/knockback and lighting from ancient water spirit and storm lasher
- Mimiron: I shouldn’t need to explain that running isn’t always the time to life tap here
- Thorim Hard mode: Siff is unpredictable and so is chain lightning. I don’t tap here unless im at full and not taking damage. If I can manage to do that when I’m on the run that’s a bonus.

It’s true that on many fights you can life tap while running without issue, but don’t oversimplify: It isn’t true to say that you can always employ the same tactic and the 0/13/58 ISL spec enhances both survivability and sustainability, both of which are important in a raid context.

Short answer in my case, yes. Worth every penny.

Not only that, but with ISL if your mana is fine you can cast a "free" Corruption on the run rather than using that GCD for a lifetap. It may not be much, but damage is damage.

what is the best rotation?¿

It's less of a rotation than it is a priority system. I would have pointed you to the first post, but as it's out of date...

Keep Immolate up, use Conflag and CB on cooldown and fill with Incinerate. You should be using Curse of Doom also.

Personally I use: LT before the pull to get the glyph buff, Immolate > Conflag > CoD (hoping for Pyroclasm proc) > CB > Incinerate.

[E: Typos]

Once the boss has less than 1 min left to live is it really worth using gcd's and mana on CoA as deep destro? Would I be better served ignoring it?

Yes, there is a topic that lists the preferred glyphs for each spec further down.

Seems it disappeared from the main page so here it is:
Glyph Choice