In your journal, does it say the Widow Maker mission is incompleted? I'm having a similar problem with another side mission where it says the mission is incompleted, but there's nothing you can do or anywhere you can go to finish it. Are you guys just going to leave that side mission incompleted?
I'm wondering if you could go back to a previous save or replay a mission (like you can do in other open world games).
I have the same problem: I got the truck and drove through the first few road blocks, then I died. I respawned with the truck and it said "Ram through the roadblocks 0 / 9", but it doesn't show up as an objective and I can't destroy them anymore. Then I died again and now the truck is completely gone... RIP