Well, you can switch to mining altcoins once BTC becomes unprofitable.

But on the other hand, the amount of bitcoins mined per month right now may not be profitable for you at the current BTC rate but, if there is another price increase/pump .. then the same amount of BTC would mean you are making a profit.

No one really thought that BTC could reach $1000+ in such a short time, but it did. So, you should keep that in mind while deciding whether to quit mining BTC or not.

I would stick to mining BTC/LTC and not bother with the altcoins.