Riley Heligo wrote: "it is still very much a likely possibility that he survived."
Yeah...no, Wesker is y'know weakened from the PG67/AW and then infected himself with Uroborous which has an increased weakness towards extreme heat, which y'know lava has...lots of it and the fact you see two rockets from an RPG go through his head.
RE1 treated him as having died cause it er...y'know had him stabbed, don't remember anything in RE2.
The developers mentioned Chris and Leon actually being onscreen together wasn't something likely would happen, they said it could but they're not entirely 100% on the idea. I don't recall anything saying that it'll never happen, seeing how they'd already interacted off screen it's not too hard to believe that they wanted to go further than there.
Okay, for the first part, while it did weaken him, it obviously wasn't enough considering he was still able to outright tank being shot and stabbed (Heck, he survived having getting headshotted by Sheva and falling out of a plane several meters high off the ground with little to no injuries. Had it truly weakened him, I'm pretty sure the headshot would have been enough to kill him, if not the fall). Plus, regarding the whole Uroboros thing, considering he managed to fight them to a stand-still (literally the only reason things ended badly for him was because he was unlucky enough to be on part of a breaking-apart volcanic surface that was giving way), and even when falling into lava, he didn't even look like he was being affected at all by the lava (and before you mention the steam bit, let me remind you that the scene where Wesker infected himself with Uroboros had rainfall being present due to the odd lines that could be seen in the background, so it's also likely that was just water evaporating), I find it hard to believe he was even remotely affected by the lava. Bear in mind, in Code Veronica, they had burn marks on Wesker when he got caught in that flaming pillar. At the very least, they could have had him looking more like Anakin Skywalker when he got a bath in Mustafar's lava pits, or Lorenzo Belli after falling into that lava pit and climbing out of it in Haunting Ground, or even how Bowser turned into Dry Bowser just to name a few examples. And all of those were on systems that were if anything INFERIOR to the PS3. If they wanted to show Wesker actually BEING affected by the lava, and not looking like he's wading in it like a jaccuzi, they should have given him the Ghost Rider treatment, no ifs ands or buts. And it also doesn't help that due to how the RPG-7s were animated, it looked more like Wesker just ducked. Besides, the shoreline was still in close proximity, and based on that virus memo, even a tissue fragment would have been enough to revive him.
As far as Resident Evil 2, there's the fact that he didn't appear, the EX file that dealt with Chris's debriefing made clear he was dead, and Birkin's memo to Chief Irons all but stated Wesker was dead.
And as far as Chris and Leon, if they say it's not likely, that means they probably AREN'T going to do it. And quite frankly, I've seen a few series where they brought back the main villain DESPITE explicitly stating he died, like Big Boss in Metal Gear (Kojima repeatedly made clear before MGS4 that Big Boss died at the end of MG2, yet he brought him back for MGS4).
Anyways, like I said, even if it isn't 100% confirmed Wesker's back entirely, it ALSO isn't 100% confirmed that he came back as a clone either, so we shouldn't assume that's what it's implying either.