I'm not an expert on Android, but your post sounds like a clear no when you consider marmistrz's 3 requirements.

Besides, comparing Jolla Tablet - an Intel device without real support that's not going to get optimized - seems a bit off. Jolla (the phone) was always praised for its battery life, as SailfishOS uses some tricks to help the power consumption, like deep sleep of apps when the phone is locked (unless the apps use Nemo Keepalive which is not allowed in Jolla Store) where apps' processes are slowed down (big simplification). One could argue if that's real multitasking, but it's nowhere near iOS/Android - you're right about that.

EDIT: I would also like to know if what marmistrz is asking about is achievable using some tricks. I tried to use a recent Samsung phone in the last couple of weeks, after my Jolla broke, but had to go back to the N900, as multitasking is definitely not the case in the Samsung's flavor of Android and downloading random ROMs (with no source code origin verifiability) from shady forums is not my cup of tea.

EDIT 2:
To share my experience from the Samsung's Android (v5.1; others may differ):

1. No, the system kills it whenever it considers necessary.
2. No, there is no multitasking screen whatsoever - you only have a "recent apps" list, but you don't know which apps on the list are running and removing an app from the list doesn't necessarily kill it.
3. No, to close an app you must go to Settings -> App Manager, find a tab called "Running", find your app, click on it and press the "Stop" button. Minimization is done by pressing the Home button, but you can't be sure it will stay minimized (see above).

EDIT 3:
To expand on the tablet argument:
My HP Touchpad with webOS featured real multitasking and when in Airplane mode, it drew ~1% of battery per night, so it could stay up for a month as well. Unofficial Android on the same device under same circumstances couldn't stay on for two days. It's all about optimization.