I think it’s too late for that. If they wanted to kill Neal to advance CS, they needed to start building it immediately. At this point, they have three episodes. It’s not enough to believably get from where they are now to TLK/proposal (which is necessary for Emma in 322 if they want to bookend the season.)
The rate the story has been moving, 3B has only covered maybe a week or so. Even if they go back in time, they’ll probably only be there for a day or so before things get switched back. And right now Emma is at “I can’t trust you” with Hook, so even if they did another “1 year later” jump at the end, there’s still not enough time for Emma to believably go from “I can’t trust you” to “hey hotstuff how about it” before a 1 year time jump to make their 1 year later relationship be believable.
And I know that people often say that Emma doesn’t NEED a romantic TL to be happy, but let’s be real, she’s their own invention of a fairytale princess, so she’s gonna end up with a romantic TL. And right now they have no guarantees beyond S4, so the endgame relationship for their herione has to be a thing they’re already working towards. And like I said, they do NOT seem to be working towards CS being grand and romantic and trustworthy TL.
They HAVE laid groundwork for SF being established as those things though, they’ve even gone so far as to give them the TL label, via the necklace. If they brought Neal back at the end of S3, they’d have that guaranteed S4 to continue developing the progress of SF in a natural, believable way. Give them TL-team moments, (like when Belle helped Rumple to give them the Glinda info), and then by the end of S4, if they don’t get S5, at least they’ve cemented the love story of their herione. If they DO get a S5, then just throw a new challenge at them and have them continue to grow together.
Back to S3, and a big TL moment for Emma in the finale would absolutely bookend the season perfectly, considering 3B started with her almost but not quite getting engaged to the guy who was lying to her about his true nature. Saying it like that makes Walsh sound an awful lot like Hook, huh. So if they wanna bookend it with a contrasting GENUINE TL moment, it really should be with a guy she knows inside out and knows she can trust, someone who has proven himself as wanting the same things she does. And that’s exactly who Neal is.
Basically, I guess this was a long winded way of saying that all things considered, the most logical choice for the story to progress in a believable way involves the guy who is currently dead coming back.