Election process if no one gets a majority in the Elec College?

[Nym90]

I believe you are mostly correct on A and B, except that if the Senate were divided 50-50 on the choice of the VP then the previously sitting VP would break the tie (since the vote would take place before Jan. 20). A state would essentially not have its vote for President count if its delegation was split evenly, but 26 delegations are still required for victory. If no one had 26 delegations (and remember the 3rd place candidate if there is one is still in contention, unlike the Senate which can only vote for the top two thus guaranteeing someone will win) then the House would have to keep voting until it could come to a decision. Likewise individual delegations could thus vote again and someone might eventually win a majority in a state to get that state's vote. If the House can't decide by Jan. 20 on a President, the VP elected by the Senate would be acting President until the House could elect a President.
But what if the VP vote was filibustered in the Senate? Or can it even be filibustered? I honestly don't know the answers to those, but then I would guess the Speaker would become acting President until someone can get elected to something.
As for C, I am pretty sure that a majority of the House can decide to hold a new election for Speaker, as the office of Speaker has changed hands before in midterm (not since the early 1930's though I believe). If the election were a tie, I believe that the old sitting Speaker would remain in office. Another interesting thing about the Speaker of the House is that it doesn't have to be a member of the House. Anyone can be elected Speaker, they don't have to actually be a representative. No one who wasn't a House member has ever been elected, but it's been tossed around before as a possibility.

[Nym90]

Well, if the President elect died before the EC voted, then the electors could vote for anyone they wanted to. Presumably the party would want to decide on one candidate for them all to vote for, because if they split their votes the race could get thrown into the House. But, the electors could vote for whomever they chose, the party would probably try to get them to vote for the VP elect, but they wouldn't have to.
Yes, Horace Greeley in 1872 died before the EC voted, it didn't really matter since he lost the election, and thus the Dems didn't really worry about who the electors voted for. The electors ended up splitting their votes several ways.
If the House is evenly divided on the vote for Speaker I believe (but am not entirely sure) that the old Speaker would continue to hold the office until the tie could be broken. Either that, or the Speakership may be completely vacant until the tie can be broken. The Constitution seems unclear on this.
The Vice Presidency couldn't be vacant though unless there was a filibuster, since the Senate must decide from the top 2 candidates and there is a provision to break a 50-50 tie (the sitting VP votes). Thus, this ensures that at worst the VP-elect becomes acting President if the House can't elect a President.

[Nym90]

Actually, it would be the new House, not the old, that would elect the President, since the House is sworn in on Jan. 3 and the Electoral College votes aren't certified until Jan. 6, so the vote in the House and Senate for President and Vice President would occur with the newly elected Congress.

[Nym90]

I believe the Jan. 6 date for counting Electors is prescribed in the Constitution, although I'll admit I'm not 100% sure.
The bullet meant for Roosevelt that killed Chicago mayor Anton Cermak was fired on Feb. 15, 1933 by Guiseppe Zangara. (They weren't riding in a car, BTW, I think you are confusing it with Kennedy's assasination). Cermak himself didn't die until March 6, 2 days after Roosevelt was inaugurated. If Roosevelt had died on Feb. 15, his Vice President John Garner would have become President on March 4 (which is when the inauguration was held then, the last time before it was moved up to Jan. 20). That definitely would have changed the whole face of history regarding the Depression, WWII, etc., although how so no one can say for sure. If Roosevelt had lived until March 6 and died like Cermak did, he actually would have been inaugurated on March 4 while on his deathbed and served for 2 days.