As I said, I don't think they'll be making whole missions centred around specific characters from ME2 if it's possible they didn't even survive. Creating content like this takes time and money and it's one thing to record a series of alternate lines of dialogue, it's quite another to make whole sections of the game that could be skipped over entierly depending on what you did during the suicide mission. This is exactly why Kaiden, Ash and Wrex only had cameo roles in ME2 since any two of them could be dead.
As for Liara, given how thing are left off if you don't have LotSB I think the only real difference in how things are likely to turn out for her without Shepard's help is that Feron probably didn't survive and she's become much more hardened after becoming the new Shadow Broker. Again, this is just narrative variation, from a functional plot POV there'd no difference. Just like with switching Wrex with his brother or Ash/Kaiden on Horizon. Sure the dialogue is different but functionally the plot is no different no matter who's playing the part.