Is there any way to track the flag/unflagging of a node/user without the Heartbeat module? Or a way to track all user/node interaction to use it after for statistics?
Yes there is a way ... using a combination of these (commonly used) modules:
Long story short:
- Create a "Message Type" that you'll use for creating some type of custom logging (for the events you're asking about).
- Use the Rules module to capture the events, with rules actions to create appropriate messages (= records in your custom log).
- Use the Views module to browse the messages that got created.
For a variation of your question, where a similar technique can be used, refer to my answer to "Is there a way to send emails when someone logs in?".
PS: this answer applies to D7 ...