Same thing happens if someone's project goes into crazy deadline mode or for whatever other reason doesn't have time to play anymore.  It happens, and I see this as just for fun.

You'll want to stick to 40 if you can. Sometimes if you need to round out your mana curve you might go to 41. A technique I use for testing out a deck is to deal myself 7 cards and play out 5 turns without an opponent. It's not perfect because you don't have an opponent but it's a quick way to feel out your deck. You'll also find that sometimes cards that sound good turn out not so great in practice and vice versa, and other times a good card just doesn't work in your deck. That just takes experience and practice. (or you could look up what others think of a card but I'm more of a learn from my mistakes kind of person)