Thanks for the kind replies.
The main point of question for me is: what altitude after reaching CLN at 6000? Remember there was no mention of altitude at all in the ATC clearance or from tower. Yes of course we were planning to stay level at 6000 after complying with all restrictions in the absence of further instruction....at least I was. However the PIC stated shortly after takeoff that he believed he was free to delete the SID restrictions because "we were never cleared to climb via SID". I strongly advised him against it, and luckily he listened.
Is not normal for clearance delivery to issue, as part of the initial ATC clearance, a level to maintain in after complying with SID restrictions (or if 6000 is the limit, reitierate such)? In the abscence of that, such altitude was usually written on the SID chart. That's how it worked prior to the implementation of climb via phraseology in FAA anyway, although it has been a long time so I might be misremembering. In this case the crew is simply left to infer that 6000 is the limit. For all practical purposes the departure radar controller issues higher level before it becomes an issue (in this case, frustratingly they did not use the "climb now" phraseology, rather simply "climb level 200"); perhaps im just being pedantic.