I'm a rotational player and don't seem to have the same issues. When I switch to a different set of sims, play for a while and then return to my original sims months later, things like the plants are still alive - their status seems to freeze when I'm not playing them and even food I left in the fridge is still fresh.
Relationships do decay though, which is unfortunate when it's romantic satisfaction added by Lovestruck - I'd like that to freeze when in the background, similar to how fame decay freezes in Get Famous. But I do also like that if I see my sims in the background doing stuff, it progresses them - e.g. if I'm playing some other family and see my original sims visiting the gym, when I get back to playing them in the future I can see their fitness has increased. That seems natural to me.
Back when I played The Sims 2, everything was frozen in state when you saved and changed household, which preserved everything, but also made it really difficult for me to keep up with playing everyone equally. I prefer the way The Sims 4 has universal time passing and how if your sims are being simulated in the background, then the relationships are changing, their stats are increasing, and they are still living their lives without you directly controlling them. That's the more realistic life sim for me.
So there's upsides and downsides to both approaches, but it really does sound like your plants dying is something happening on your side, possibly due to gameplay style - because it's not happening in my game, e.g. if I'm not playing a household, then I don't visit their lot at all - any time you have them on screen, time is passing and things are decaying/changing.
