If you spilled weed killer concentrate, the spots it hit are probably dead. That is many, many times the concentration they can handle.

What chemical? If it's Glycophosphate (Round Up), then yes, the grass is gone, and according to the label you should wait 7 days for the residual herbicide to decay before seeding.

If it was a 3-way or similar (2,4-D + MCCP, etc.) you're looking at more like 3 weeks.

For the tomatoes⦠for me, it would depend on how many plants you're talking about. If it's a couple, I'd go ahead and replace just to be safe; plants are cheap. If you're talking 20⦠maybe that's a different story.

Around here tomato plants don't do much growing anyway when nighttime temps are still below 55 or so. In my garden, they don't go in the ground 'til the lettuce bolts. :-)