If one can have it on an external drive it is strongly advised to keep a working OS X installation at hand.
There a just a lot of things that are easier to do with the designated OS.

If you have even an installation with more working professional apps, like Office, Photoshop or somethin, keep it.

Of course if you are a long wintered Mac user you must preserve every generation you had as a working bridge system, anything else would be silly!
😉