Although they like to kill main characters I get the feeling that Tyrion might be the one of the few characters that will carry the story through to the very end. Since he is the best character by far this may be wishful thinking but I'm going to go with my hunch. I also think that the dragons must be part of the end game so Danerys must have a good chance of surviving to the end.
If this guess is true then who is going to die in the next 2 episodes?
John Snow? I'm thinking not as his and Sam's storyline seems to be important for the wilding/white walkers part of the plot. If the Wildings slaughter everyone then the North is very vulnerable. I therefore expect the Night's Watch to beat or more likely outwit the wildings thus slowing this part of the plot somewhat. Maybe they will block the wall/tunnel up and fall back to ???? Take Winterfell?
Tywin Lanister is a great character but he is so powerful and manipulative that it would take quite something to get rid of him but if he was dead the plot could move with a bit more freedom. More poison perhaps? The bald eunuch to allow Tyrion to escape? Given we need a shock death of a really major character I think he is at least possible.
Jaime Lanister - rapist, child attempted murderer, incest enthusiast but nice to tall female knights and his brother (sort of). It would seem an odd time to kill him as his life or death wouldn't move the plot along much at the moment.
Danerys Targereon = Tits and dragons. Not going anywhere.
Reek - who cares? Could be an easy major character to write out
Cersei Lanister - nasty piece of work, should die horribly therefore won't. Not yet at least. I think there is more to her story yet so low death chance.
Various young stark offspring - all seem important for now so will probably survive
Tall female knight whatever her name is and the former serf to Tyrion have only just started their journey so probably won't die
Hodor - hodor hodor hodor
Bron - seems to have just started a new storyline so low death chance.
Petyr Baylish - surely has a major plot arc to go so won't die.
Ygritte - may have become superfluous once John Snow did a runner. Maybe not and may join up with John again.
Leader of the Wildings could be in danger as a fairly generic baddy
Annoying bloke who lead the Knights Watch is probably going to die to allow John Snow to do whatever John Snow is going to do next.
Fat Sam and his woman and baby. You lot hate them so they will live.
fat bald eunuch and the expelled knight seem to still have plot importance so probably safe.
So my guesses at chance of death are:
75% Annoying bloke who lead the Knights Watch
55% Leader of the Wildings
50% Reek, Tywin Lanister, Ygritte
25% Tyrion
20% Jaime Lanister
15% John Snow, Hodor
10% Tall female knight whatever her name and the former serf to Tyrion, Cersei Lanister, all the young Stark offspring, Bron, Fat bald eunuch, knight expelled by Daneyris
5% Petyr Baylish
2% Danerys Targereon
1% Fat Sam and his woman and baby
So 2-3 of the 5 characters I've rated at 50% or above would be my guess unless Tyrion ends up dead. I suppose only the 3 at 50% are really main characters so maybe 2 of them if Tyrion survives.