This may seem more like an alternative philosophical approach than an answer, but I do not design encounters with the makeup of the party in mind beyond their level & party size. 

If a group of players choose classes that aren't "balanced" with each other, in my opinion it's up to them to adjust their tactics, not you. They might choose to start being more careful and set up ambushes instead of leaping into the fray. They might choose to hire some muscle or build a golem or find some non-player thing to fill the role of "tank." They might choose to avoid combat every now and then. But I personally believe that you needn't make too many adjustments on your end, and instead keep focusing on designing encounters that are logical and consistent with the game world. Every time I run games for an "unbalanced" party, they always figure it out with no intervention on my part. 


The usefulness of this answer may be entirely dependent on your group, but in my experience you should never underestimate your players' ability to adjust on their own to new circumstances. 

All that said, if you're *still* worried that your players aren't equipped to adjust to their new circumstances for whatever reason, then I suggest testing that hypothesis. Scale down the challenge of your encounters just a little—without changing the actual mechanics—and watch them learn the lessons they need to learn in a somewhat less lethal space. Use the same monsters, but maybe reduce their numbers or their HP or their damage just a little. When you feel comfortable that they've figured out their new limitations, you should be able to confidently crank the difficult back up to the level that you normally would design to.