Blizzard Beach is near the Animal Kingdom, the All Stars and the Coronado Springs resort. The Beach Club is right by Epcot - different area of WDW. You can definitely leave the park and come back. However, I do not think eating at Beaches and Cream for lunch makes any sense during your day at Blizzard Beach - not a good use of your time. When you are at the water park for the day, you have to change into your swim suit, get situated in chairs, get your sunscreen on, rent a locker (usually), etc., and in order to leave, you would have to get dressed, dried off, pack up everything, and walk a LONG way down the hill either to the buses or the parking lot. If you are doing buses, then you wait for a bus, and take the 20 minute ride (including time to drop off at other resorts) and then go to Beaches and Cream. Then you wait for a bus back (could be 20 minutes or so), take it back, and walk all the way back up to the park (uphill to where the slides are) and try to get another place for your family to sit, etc. This will cost you 2-3 hours of real time. And you will probably just eat burgers at B & C - which is same thing you will likely eat in the park at Blizzard Beach. Save yourself the trouble!
By all means go to Beaches and Cream, just not as "lunch" in the middle of your Blizzard Beach day. Plan to eat at Beaches and Cream on the day you visit Epcot - you can exit the International Gateway at Epcot and just walk over and get lunch or dinner at Beach Club, then return to Epcot. Alternatively, eat dinner at B & C after you are done at Blizzard Beach.
Just my 2 cents!