While searching for research groups pertaining to my area, I came across one that matched my interests well. But in the publications page, the most recent paper was written in the year of 2015, which was also the last paper by the professor. There are no indications that the group has been discontinued. As for the professor, he seems fairly active until last year (but no papers), according to his bio. I tried to get in contact with the university regarding the activities of the group but I didn't get any response yet.
As for the students in the group, there isn't much information about their recent work. The university is pretty well ranked and my research interests align with the group so I'm hesitant to let this university slide but since papers are good indicators of how active a group is, does it mean it's better to move on? I haven't contacted the professor personally regarding this since I wasn't sure how to go about it. (I came across this and am considering sending him a mail.)
In general, are publications the ultimate measures of performance or is there a useful rule of thumb for choosing or not choosing of a research group/professor for PhD (apart from the publication list)? I'm not very knowledgeable about the process yet so any help on this is appreciated.