Honestly, Riot had a few reasons for changing Zyra's post-mortem passive - for one, having a passive that relies on dying to do something is bad enough, as it incentivizes reckless play, and it was made even worse that you only had one shot, unlike Karthus' being able to cast his spells or Sion being able to drag someone down with him.
And, also, don't quote me on this, but I think I recall Riot saying that the post-mortem Passive and official death animation made it fairly difficult to produce skins for her - but again, I could be totally wrong in saying that.
And, on top of all that, it is better that her current passive drops seeds near her consistently, because it opens up a lot more options for play. It's no longer just "drop seeds and throw a spell", or "drop seed as bait, throw a spell", it's more along the lines of "do I rely on my passive seeds to present threats, or use them as bait, or use them as zone control? Do I want to add some more seeds, or should I combo them in certain ways", etc. Having a lot more seeds out on the playing field opens a lot of options for both Zyra and her opponents.
So, in the shortest sense, I think her current passive is fine, and I don't think she needs her old passive back.