I haven't read the whole 14 pages of the thread but here's my tuppence worth: personally I would not leave my youngest behind. I would not be able to relax and have quality time because i would think about my youngest, worrying if she's missing me (I would assume that yes she does), if she's upset etc.( I just assume the baby is a girl for no specific reason)
I know that a child that young, cannot make reasonable assumptions and to her, not being with mum is an unusual situation where she has no idea if it's temporary or not. All she'll think about, is that mum is not here and not sure why and not sure if coming back to me again. The rest of the closest family are not here either, so to her it's a stange situation to be in. Stressful.
When you come back, expect her to be distant towards you and a lot clingy and tearful. It'll make you feel bad and you would remember that feeling long time after.
Whether she'll remember being left behind in the long run, i wouldn't know. But it definitely will create stress for her in the short run.
Your mum might do a wonderful job but a child age 2, needs her primary care giver more than anyone else.
Personally i wouldn't leave her behind for that period even with my own lovely mum, unless it's absolutely essential. And in your case it's not essential, it's a luxury, in my opinion.
Wouldn't it be lovelier to go as a whole family, have photos with all of you are together, to remember this in the future. I'm sure whatever stress you'll have when baby is with you, will be forgotten about in a few weeks or months time but lovely menories and family photos will remain.