The fact that Wally had zero presence in Season 2 and that he didn't have to die, and he did die, in the finale of all episodes, makes it extremely obvious to me he was meant to have a large supporting role in Season 3.
I can't buy into this... There's no way they would 'cheat' the viewers by having an emotional 'death' scene in a season finale, only to bring that character back for a large role in the next season. Now, maybe he could've returned towards the end of season 3, sure, though his return would have to come at a cost, otherwise "Endgame" would be robbed of its sadness. Perhaps he would be revived as a significantly older version of his former self. Or maybe he would be exactly the same, while a significant amount of time would have passed for his friends and family. The latter seems more likely to me, because it would be a punch in the gut if he was the same old Wally, ready to pick up from where he left off, but finding that it's impossible since everyone (including Artemis) had aged and changed a lot. It would be like Starfire's predicament in the Teen Titans episode "How Long is Forever?". But for this to really succeed as an emotional twist, lots of time would need to pass, not just 3-5 years. So it seems to me that Wally might have come back in season 4, not season 3, when Artemis could potentially be as much as 10 years older than him (or more), with no hope of the couple reuniting. It would have to be done along these lines, or the season 2 finale would lose a great deal of its purpose. The longer the crew behind the show were prepared to wait to bring Wally back, the harder it would be emotionally for the character to fit in when he DID eventually come back, so a return in season 4 or even season 5 would work better than a return in season 3.
Think of Artemis and Bart's poignant conversation on the Watchtower in "Endgame", from the dialogue to the music. I can't see the crew rushing to undermine this scene in the very next season.
We should probably also consider that maybe a Flash
did have to die... Earth-16 is a parallel universe where some choice deviations from the timeline of the comics has a butterfly effect on how everything plays out. For example, Kaldur'ahm becoming Aqualad instead of Garth. Garth was still there in this continuity, he could've still become Aqualad. But he declined: a small, decisive moment which changed everything for this continuity. Likewise, in the finale, Wally dies, in what was obviously supposed to mirror Barry's death in the comics, I believe. Key events from the comics were being adapted, and the death of a Flash was one of them. With the whole world threatened by the MFD, this was a good time for Greg and Brandon to play that card.
At least we agree that Wally would've come back though! I think the next step in Artemis's story would be accepting his passing (even though it would ultimately turn out that he's alive). And then on his return, they would have to deal with seeing each other again but not being able to reunite as a couple due to the age gap. "Endgame" may not have been the end of Wally, but it was the end of their relationship, just like young love can come to a cruel, abrupt end in real life.