The sentence in question is a "partial" sentence in which the main verb is omitted. Similar things happen very often in English, too:
Did [you] come (here) often?
Yeah, when Dad was still alive ([I] used to come here)...
(The subject may be "she" or someone else instead of "you/I".)
The "full" version of the sentence is お父さんがまだ生きてる頃はよく来た, but よく来た is left out since it's redundant. This は is a topic marker, and it's almost mandatory here because it has a contrastive nuance (i.e., now this person no longer visits the place). ね is just a sentence-end/filler particle.
BTW, please try to provide the full context when asking a question like this. No one can tell the omitted verb without the context.