I had the same thought. However to put things into perspective, Shire and enanta are not comparable.
Shire's offer is meant to bolster abbvie product line which will see a generic humira soon or soon enough, whereas enta's offer and integration would happen seamlessly as abbvie already runs all the trials.
Also the magnitude between the two offers differ greatly. I would be ecstatic if the offer is somewhere between 1B and 1.5B$.
I would wait next yr for a few months to see how abbvie/enanta combo revenues stack up and if no offer from abbvie within 6mos or so I would seriously whittle down my stake.