Hextech Gunblade is the only option for AP champs to sustain?

Ravenous Hunter nets you 12.5% spellvamp when it's fully stacked, doesn't it?

So, short answer: yes, it's the only option similar to lifesteal, but don't forget Catalyst and its upgrades with the Eternity passive.

Long answer: Spellvamp was always a pain in the ass to balance properly for all Mages/AP Champs at the same time. No matter what Riot tried, only a couple of Champs ever bought it (usually Vlad, sometimes Ryze). So they decided to remove Spellvamp from items, and only Gunblade was kept. The trick with Gunblade is that the AD it gives serves as a tuning lever to control who can or cannot use the item. Most Mages won't want to buy it because they are sinking too much gold into a stat that they can't properly use, and if Riot want to make Gunblade a good buy on a certain champ, they can just give them AD ratios somewhere (or buff the ones that are already there), like they did for Katarina's rework.

health pots!!!!! :D

I love gunblade on Ahri, I can sustain most my life without passive on 1 wave with q and w

Yes. Gunblade is the only item for damage-based sustain (which works not too well with casters that are not balanced around sustained damage).

However, for general sustain, APs also have and , both of which inherit 's mana expenditure -> health mechanic.

It's time to bring back spell vamp.

Who cares if Vlad and others abuse it? Certain AD champions practically get their health back with one auto/ability. If AD champions are allowed sustain, then so can AP.

With grevious wounds abundant, there is plenty of counterplay to healing.