Story Mode Misions can be attempted indefinitely until completed once. Each attempt reduces the available resources of the mission base depending of destruction of the previous attempts.
This has been subject to change recently and many "Character Crystal" Rewards were changed to "Mixed Crystal" Rewards while many "Premium Crystal" Rewards were changed "Character Crystal" Rewards or fixed Transformer Rewards like Chapter 1.
Below list all the campaigns until current version with 5 missions each campaign. Rewards vary but include alloy, energon and both premium and Special character crystals such as "Leader Character Crystal" that grants the factions respecive Leader Transformer (Optimus Prime / Megatron ) as a Rating. Story Rewards are given after completing certain Story Mode Missions.
No time to waste, the Decepticons are here! We must find a way to get our Leader to Earth
No time to waste, the Autobots are here! We must find a way to get our Leader to Earth