Can you say "好久不看“ in written conversation?
I assume you want to use "read" because it's written conversation, but you want it to have the meaning of 好久不见, am I right? If it is so, then I think it would be better to say “好久没收到你的消息/来信” (It's been a while since your last message/letter) or “好久没联系你” (It's been a long time since we contacted each other).

“好久不看” is grammatical, but it seems to me that it would not be natural in the situation you described. Some certainly good use of “好久不看” would be (all the examples are courtesy of Google):


  好久不看球了 I haven't watched a match for a long time
  
  10几年前一直看动漫，好久不看现在该去哪里？ 10 years ago I used to watch anime all the time, it's been a long time since I watched it, where should I start?
  
  好久不看这样的电影了 I haven't seen a movie like this for a long time


And so on, so on. At first glance it seems like “好久不看” is often used as "it's been a long time since I watched/saw" rather than "read".