and it had very tiny, tiny white bugs in the rootmass. Anyone know what these bugs are?

Wish I could be of more help, but I have no way of knowing, especially without a picture.

Did they cause death of plant or were they just a result of the plant being weak?

Hard to say; but if I had to venture a guess, the guess would be that there were problems with the plant (likely root rot) and then whatever insect it was moved in and started eating the decaying parts of the rootball.

And...what can i do to prevent it from happening again other than plant in different beds next year which i plan to do.

I wouldn't necessarily assume that you'd need to plant in different beds. Are you seeing the bugs in the soil of the current beds?

I'm gonna pull the other plant that was beside it up.This time i'll have my camera with me.
Don't know about the root rot or not. There are 2 other plants in the bed with them. One is a Abraham Lincoln, it was struggling for a bit but seems like it might be bouncing back. The other is a Stripped Stuffer and it is growing like wildfire. Also, the order of the plants in the raised bed is Boxcar, Boxcar, Abe Lincoln, and S. Stuffer. They are approx. 4 ft apart.
I havent noticed any bugs in the soil of the beds, but i havent really looked. The beds have a drip irr. hose laying on the soil around the plants, then a layer of newspaper(about 6 sheets thick) and then a layer of mulch. So i don't really see the soil. I guess i need to get out there and dig around.
I'll try to post some pictures in the next couple of days if i see the bugs in the next plant. It's gonna be taken out because it's toast too...lol.
Thank you for your response, you have given me some things to think about as far as this goes.
Thanks again,
Peggy