I am working on Heartache by the Number with Cassiday. I need to go the VanGraffs to steal some evidence. My question is if there is a non-violent comclusion to the Heartache quest, will this impact any future dealings I may need to do with the Van Graffs. How far will the program allow you to go before you end up doing something that affects other story lines...like the main quest?

There are quests that can severely hamper your reputation with a faction, and if that's the NCR or Legion and you're trying to complete the game through one of these factions that can really throw a monkey wrench in to the works.

My first character went the NCR route and also had Cass. If you choose the more violent path for her quest you will damage your NCR reputation but this didn't prevent me from completing the main quest. I haven't done the quest the more peaceful route so I'm not sure what the impacts are.

Yes there is a non-violent way to get through this, use a stealthboy to break into the Van Graff safe, and the same for the Crimson Caravan safe, then you have ample evidence of corruption - Cass will speak to you when you get the evidence, just talk her down from her want for revenge (may need a speech check, can't remember exactly) by telling her that reporting it to the authorities (NCR) will have a bigger effect on both guilty parties in the long run.

ETA: having said that it is probably not a good idea to take Cass should you meet with the Van Graff's for any reason in the future, she may have quieted her demons, but they may still want her dead - haven't tried it myself but it seems logical to have her wait outside for future transactions with them!

Thanks for the reply. I finished the quest without any negative results. I was worried that the Van Graff place would figure into other quests down the line, but I used a Stealth Boy and they never saw me!