That's a very complex question, and I can only answer for myself as I am in this moment in time.
And right now, my answer is that if something conflicts with Shabbat, Shabbat wins. The only exceptions are for medical and similar emergencies - you sacrifice one Shabbat so that this person can have many more (or so there is good will in the community.) And even then, you try to minimize the violations as much as possible, so long as that does not prolong the emergency. If it's a situation that can be planned - a pregnant woman, for example, might well go into labor on Shabbat - people seek rabbinic advice on how to minimize the violations. Timing was a major issue for my first IVF attempt, and we made sure to talk to a rabbi about that (and everything else.)
In large part, it *is* that I wouldn't violate halacha without good reason - and doing so deliberately is, of course, far worse than doing so accidentally. And you really can't say, "I'll repent later." It doesn't work that way - you probably won't be truly repentant.
But I've lost a couple of Shabbats to poor planning or family emergency, and it's a punishment all by itself to us. I've missed it terribly.
When I'm at a convention, I do a few things to remind myself it is still Shabbat besides just trying to avoid violations. One thing is that I tend to dress in Shabbat clothes instead of con clothes. I leave the t-shirts packed away until Saturday night, and wear things I'd wear to shul instead.
Shabbat is a *huge* deal to observant Jews. Everything revolves around it. A few weeks ago, Yom Kippur, the highest of the high holidays, fell on a Shabbat. It's a day we spend in prayer and fasting - tremendously spiritual. But it didn't feel like Shabbat, and everyone I've spoken to has felt the same way - we lost our Shabbos that week. Honestly, with all the three-day holidays, last week was the first *real* Shabbos in a month, and it felt good.
