Bio Hazard 'Save-Room' themes are usually effective at breaking the tension of getting munched by zombies... or in the case of Zero, by leeches.
While sticking close to the (short) source material and spreading it over an extended time span, you've managed to build a strong feeling of loneliness.
The samples could work if the soundscape was busier, but the fact they're completely exposed won't fool the mods or the audiophiles for very long.
Delay effects are little too rigid, and since the strucutre is based on repetition, it gets flat after a while somehow.
Some gentle strings might help support the piece, rather than leaving all the work to the piano-string sample.
As for the ending SFX, I'd say: keep the rain/thunder, remove the birds (if you can), crossfade-in, and drop a few db in the process.
That being said, I enjoyed this calm and moody, quasi Yamaoka-esque take on the theme.
With more polish on sound-design/prod and the addition of a few breaks for a change of pace, this could end up being a pretty neat arrangement.
And if this is indeed your very first foray into remixing, then kudos for taking the time to craft a song that needs to be enjoyed slowly.
Emphasis in the OP that it's an AMBIENT piece, so that people don't get stuck waiting for any crazy synth-solos, guitar shreddage or unts unts.
Keep at it and good luck.