Lanefan
Victoria Rules
Whose "general social contract" is this?The general social contract of play is that the new character gets slotted in to the party without any fuss, regardless of the party dynamics already at play.
If your only PC dies and there's no logical in-fiction way to bring in a replacement right away then sorry, you're gonna have to wait.
Further, there's nothing saying the new character has to - or will - fit in with the existing dynamics within the party. Most of the time a new recruit is a complete stranger, not knowing and unknown to the party before now; and while the party can conduct what amounts to an interview process and accept or reject any who apply for recruitment (I've seen this done!) oftentimes you just gotta take what shows up.
I'm in between on this - a new character usually comes in a level or so below the party average. (exception: if it's a player's first character in that campaign it'll come in at the average)They're not going to be "back to basics" besides the fact that they don't have the past experiences of the campaign behind them; punishing a player whose character died by giving them an even weaker PC (if that's what you're implying) is just nonsense outside of any game that isn't some OSR games.