I'm replacing my guides, Vanos, chains, etc., right now. If your guides broke apart you most likely have some damage to the chains which may be minor or may be significant but you can't tell until you get the covers off and look at them. As mentioned, if you're already changing the guides, the chains are not that much more work and the cost for the chains compared to a failure is IMO small. Either direction you go, I would highly suggest that you get a new chain tensioner (part# 11317531813)
If you do replace the chains you are going to have to reset the timing which you probably already know and are probably trying to avoid. If however, you have to replace the chains because of damage watch this video it helped me understand how to use the tools and how to set the Vanos.
RE: BMW Vanos Repair - YouTube