I agree that no Corleone would take someone to court. Vito's whole way of life is based on not recognizing the legitimacy of the courts over him and his. Vito would view going to court and begging strangers to intercede in your life as contemptible.

Tom's only concern was to ensure Vito was kept safe until he could be moved to the mall. So Tom used his seeming upperworld status to impress upon McCluskey that further interference at that point in time would be met with superior (legitimate) political force.

Maybe over time Tom and Sonny might have been able to use their father's judicial and police connections to get McCluskey transferred to a highly undesirable location, mess around with his pension, get him kicked off the pad or something like that but as Michael pointed out they had no time.

In order to save Vito's life Sollozzo had to go immediately. As there was no way to do this without also removing McCluskey, the cop got to go along for the ride. I think it was business and personal for Michael.