Generally, airline or hotel points earned from an affiliate credit card will not be forfeited upon account closure. Those points are stored with the airline or hotel, not the bank. Rewards that pertain to the bank itself (like Chase Ultimate Rewards, Amex Membership Rewards, Citi Thank You Points, etc.) are often forfeited upon account closure. There are exceptions to both cases, so contact the credit card issuer for verification.

I'm with PainCorp in response to your second question. You need to put the time in to fully understand how churning works.