In a patch a while ago they took out the ability to macro "ifhasbuff" or some such like that, as people were making addons use that for automation (Decursive used to be mash one button, win at internet).

You won't be able to use castsequence to bypass the weakened soul debuff, as it will stop on trying to cast bubble, and will not let you use renew until it's able to cast bubble.
Your best bet is to use a modifier and just watch for the debuff on party frames.

/cast [nomod] Power Word: Shield; [mod:alt] Renew