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Here's the reason for the non-crash, imo:

Desmond, as seen in Flashes Before Your Eyes, wound up in his body, at time when he and Penny were together, with fragmented memories of having been on the island. Not just having been on an island, but having lived through the period of time we saw him in.

It caused his memories of the soccer/football game in the bar, and of the bartender getting hit in the head by Jimmy Lennon with a cricket paddle.

This episode...

Here it is Doc. You asked for it

Spoilers are present thru out. Just a warning to non-spoiler hounds. If the button threw you off.

ETA: apologies to anyone who got spoiled because I put quotation tags instead of spoiler tags.
...

Re-reading the first part. Left something off it.

Basically, I think that Jughead can be detonated in 1977 and the Swan can be built. Yet I also think that the losties going back to the seventies has influenced events in ways similar to Desmond in FBYE. Nothing they do, even Jughead, negates the Swan or Desmond or the button that brought them there.

The rock solid, unchanging theory for this week

Thanks to Apopheniac for the link corrections...

PART...

As a homage to Stephen King, and because I think it's fitting to events we've seen to date. I think the first episode of season six and/or the finale may be titled:

Resumption.

Definition:
Main Entry:re·sump·tion http://www.merriam-webster.com/images/audio.gifPronunciation: \ri-ˈzəm(p)-shən\ Function:noun Etymology:Middle English, from Anglo-French or Late Latin; Anglo-French, from Late Latin resumption-, resumptio, from Latin...