It's hard to tell without seeing the individual kid's kip+cast, because some kids will do a better (stronger) kip while trying to connect even if cast is low...if they stop they might pump their legs and do an extra swing...so it's hard to say. Stop deduction definitely .3, I don't have the page in front of me right now but I thought cast was up to .3, so I guess in that sense if they do a dead stop they're probably going to get the full .3, and if they connect kip + cast (assuming it's a good connection) and at least get to clear support it would be somewhere less than .3. But, if it makes the BHC and underswing bad, then you have to take that into account.
But in terms of coaching, this is a place where I value the connection over the score, hoping the kids will get stronger the more they practice and being able to develop cast horizontal and above. I never want to see a dead stop in a bar routine, especially when we're in the process of developing kip cast. But, if they were really able to do the BHC, underswing, swing back better without then I could consider it...I don't usually see a noticeable difference unless the kid is really struggling to kip cast, although that's common (in which case they usually are still working on the jump + long hang kip - esp if they're small - and I'm just happy for them to get up over the bar with straight arms and continue the routine). Even though long hang kip can theoretically be easier when done correctly, a lot of kids can do kip cast on the low bar, but adding in the jump can cause more difficulty plus controlling the bigger swing.