It's always a good decision to remove inactive people on your email list. But before you remove them simply send them to a new campaign, then create 3 follow up emails.
Day 1 subject line: Are you still there/alive/breathing?
Then in the email body tell them that they've been inactive from 22 January 2014 (for example) and you'd like to know if they're still interested in getting your emails. If they respond then you move them back to the email campaign that has your newsletter.
Day 2 subject line: You're costing me a lot of money
Let them know that your autoresponder charges you depending on how many subscribers you have. So if they're not interested they should let you know and you'll be happy to remove them and save a lot of cash.
Day 3 subject line: You've been deleted
This subject line always gets a big open rate hehe... then you let them know that you have removed them in your email list because you're paying for someone who's not interested. Now, some people may see your email later, or maybe they're on vacation when you send that email.
So at the end of the email you say something like: "I have removed you from my email list but if you still want to get the newsletter you can subscribe again using the link below...
" then you create a special page for them with some added bonuses.
Most people will subscribe again and be more active that way. That's what you must do instead of just deleting them, you can also ask questions in email 1 and 2 to find out why they're not active. Then implement what they say to your newsletter so that you can keep more people active.
How you identify inactive subscribers and the specific date they last opened your emails will depend on what autoresponder you're using. I use getresponse and the process is really easy.
Wait a couple of weeks then remove them. keep the inactive campaign with that follow-up sequence for the future so that you don't keep repeating the same process.
Hope that helps