A while ago, a friend of mine spent some time brainstorming story ideas for a tv series for a production company. They paid him, but he's not sure if they guaranteed him a script.
First of all, if you're not sure, they likely didn't guarantee you anything, unless your agent is pretty sharp. (Agents are supposed to be sharp. But they're usually only on the top of their game if you follow up. They know agenting, but you know the specifics of your meetings with the producers. Leave the actual negotations to your agent, but keep your agent educated about what's going on.)
Second, assuming you're a bona fide professional tv writer, you should never brainstorm episode ideas unless you're guaranteed a script. If you're a good enough writer to come up with ideas, you're good enough to write a script. There was apparently some weasel language about "subject to network approval." Considering you'll be rewritten by the showrunner or head writer anyway, it shouldn't matter whether the network approves you.
This is not true if you're an assistant who wants to break in -- then you're lucky if they want you in the brainstorming session and you should give it your all.
It's also not true if you're doing this for a friend who's a showrunner. They'll probably give you a script anyway, and insisting on it contractually might hurt the relationship.
But otherwise -- your ideas are valuable, and you should get paid in scripts.
My friend wasn't sure he wanted to write for this particular show, hence his diffidence. But WGC scale for an hour show is worth minimum twelve thousand bucks a script, after production bonus. And free lancers only have to turn in two drafts and a polish. So it's almost always worth it to get the script and do the two drafts.
The hard part is getting the work. Doing the work is just the fun part.