Answer:
No, the plan will not work.
Step-by-step explanation:
This answer is just logic and considering possibilities.
It seems like they are missing decoys. Decoys can distract security outside and around the building and make it easier for the main team to get in undetected and spread the black powder. Also, if the terrorists do it in the basement of a popular location, someone will likely discover them. And if they go to the basement of a popular location, they will be checked for weapons and possibly dangerous items, like matches. Popular places have good security. So unless they manage to evade security and consider all possibilities, this plan will fail.