Sure, I'd make a new character as well, though I'd expect it to come in slightly behind those already present as it hasn't done as much in play. I wouldn't bother asking the DM whether my rescue is imminent or not, however, as IME the DM has no way of predicting whether a rescue will soon be mounted and-or whether it will quickly succeed. (as a player I once did just this; asked the DM whether I'd soon be found/rescued by the party, the DM said it was highly likely I would, then the party - not knowing where I was - proceeded to go everywhere in the dungeon except the right place)
If-when my original character does get rescued some time later, though, now I've got two PCs in the setting.
Experience points are, as I've always seen it, given for what the character experiences and-or does in the fiction. If a character can earn xp for doing nothing, where's the incentive to do anything or take any risk?
Agreed that missing players' characters can earn xp, provided the character remains in play as normal and is contributing to the party. You don't earn xp for sitting home in the pub or standing outside and guarding the horses; and integrity-to-fiction means characters don't mysteriously vanish for a while just because their player misses a session.
I should mention, in case it's not already obvious, that I don't give a fig about keeping everyone at the same level. IME other than when they first start out all at 1st level, having everyone happen to be the same level in a party in exceedingly rare.