Yes, there will be limits.. But the limits are high enough for practical purpose.. 
Participants can take several forms:
- Organizations with a separate identity and potentially with their own CA, MSP, orders, endorsers, and committers in any combination
 
- Roles in chaincodes
 
- Identities with a specific role in an organization
 
But you can set a small limit if you want.. 
And, there rollback (ACID compliant, example) if the submission of a transaction fails.
The rollback will only return a success or failure.. It does not make any changes of the failure on the ledger..
There are mainly two modes of failure:
- Fail during endorsement
 
- Fail during commit