Don't panic.
Nobody is going to miss out on Commander Luke because R2 came back early. Every Commander Luke event so far has had a concurrent R2 event.
There is no need to stress.
Now, working toward Empire is a fine and reasonable idea. If you want to try for R2 this time around, I will suggest Magmatrooper for the simple fact that they are the more reliable farm, at a guaranteed 15 shards a day any day you can beat GW, and Magmatrooper will not compete with other cantina farms.
Even if you only get five- or six-star R2, you can work on leveling and gearing him at your leisure until the next R2 event comes around, and if you want R2 for any particular team other than heroic events and last phase territory battles, R2 is entirely usable below seven stars. Star rating is one of the least important aspects of a unit's power, after mods, ability ranking, and gear. Tanks and supports especially work fine at lower star ratings.