Is it possible to permanently miss Praxis Kits?

Are there any Praxis Kits which become inaccessible after a certain period of time?

If it is possible, do any missions contain Praxis Kits?

Solution 1:

Yes there are a few Praxis kits, that becomes inaccessible, if you don't chose the right paths in a mission, or simply in a location you only can access once.

These Praxis kits are:

1. Milwaukee Junction (Factoring labs)
   • After exiting the elevator from the Assembly line you will find a Praxis kit right infront of you.
2. Bar Tab (Side mission in Hengsha)
   • If you convince Jaya to return the implant, no Praxis kit will be awarded.
   
   As pointed out by UsrbanEsc, you can still get the Praxis kit by stunning/killing the bartender, and looting him.
3. Shanghai Justice (Side mission in Hengsha)
   • If you kill Lee, Malik will not give you a Praxis kit as a reward.
4. Tai Yong Medical (2. floor)
   • On the second floor of the actual Tai Yong Medical building, there's a hidden Praxis kit in one of the desk drawers.
     Video walkthrough
5. Picus (Montreal)
   • When you enter the news station, and reach the main office floor. Go down to the cubicles, and in the center left desk drawer, of the center row you'll find a Praxis kit.
6. Panchaea
   • Deep inside Panchea there's a hidden LIMB clinic behind two vendig machine

Solution 2:

Yes.

For example the first mission (to the Sarif factory) contains one, as do your visits to Tai Yong Medical and Picus (and possibly more "mission" locations), all these permanently lost when you leave the respective levels if you haven't picked them up.

A few side missions in the city hubs also award Praxis kits. Given that side missions expire permanently when you leave the hub, these kits can be lost if the side mission is not completed before leaving.

And, obviously, those kits found hidden around the city hubs are lost if you haven't collected them when you finally leave the hub for the final time.

This includes kits that may be purchased from LIMB clinics. If you don't buy them, they're gone forever once you leave the hub - even if you return to the same hub later the clinic will only have 2 new kits, the old ones are lost.