Here is an interesting article on Moneyville by Ellen Roseman -- Don't lose reward points to inactivity
Yes you can lose value of hard earned points if you don't follow the rules. I have personal experience with Sears Club points. I did not lose a lot but lost few points. But when I called they were able to reinstate the points expired in the last 3 months.
Some times there are easy ways to keep your points active.
1. Buy small purchase to keep the account active
For example Aeroplan Miles, you can just buy Quacker or Tropicana products with Miles code and use that to keep your Aeroplan points active.
2. Transfer to different reward points. For examples Sears Club points can be transferred to Petro-Points.