Anyway its the same problem whether or not they work from home - some people will underperform and have to be let go.
Finally, use some collaboration software and folks 'working from home' or from other sites will seem as connected as people working in the office. Even more so - a meeting of remote workers works better in fact, because each one has a headset and can be clearly heard and distinguished. Instead of for instance a crowd of people 'in the office' sharing a desktop microphone and heard as a babble by everyone remote.
We use Sococo (I work there). Its got the best presence information in the industry. Its clear who's working and who isn't. You can see everybody in the area, who's active and who's idle, whom they are talking to and what meetings are going on. Managers love it!
Working 'remotely' for 5 years now, in a company where everyone does it. Its superior in almost every way.