What will happen if your spouse (wife) dies ?
Can you mary again ?

You will die old and alone and childless, because there is no remarriage in Skyrim.

(Barring mods and/or console commands if you are on PC.)

When Maramal says "Now and forever", he means it. That dude does not mess around.

Sorry, I could not help myself. To answer your question, OP.
No. It's a one shot deal.

Kind of svcks. I just know Ysolda is the kind of wife I'm going to grow to hate over time. We'll have a bitter marriage in which I purposefully avoid visiting my Whiterun home simply to avoid her.

I was away for a while and my brother decided to initiate gay marriage with Farkas. Had to revert to a backup save 5 levels earlier.

You can't remarry once you spouse dies and you can't have multiple wives. It is possible with the use of console commands to "divorce" by reseting the status. I'm sure there are multiple wife mods available.

I'd advice to avoid Housecarls unless you want them to refer as a thane and feel like a slave. I prefer Aela though, and she's my follower for quite a while now, I never dismiss her at all.

Damn it auto-correct

Damn! That scenario sounds eerily familiar...

http://www.youtube.com/watch?v=KAKaJE4gjYg Sorry, couldn't resist

BINGO!

"Tell him what he wins, Jonny!"

When your wife dies you are blessed to eternal happiness. Also a mountain of dirty dishes/laundry will slowly form.

Thanks for all the answers. It seems Ysolda is the best option becasue you can not take her as a follower (so she will not die) and I'm quite settled in whiterun (it will be easier to collect the money out of her)

If your lucky her head will land in your trophy case