going from demo to affFollow

hey i've been demo since i started my lock but now that he's about to ding 70, i want to change it up and try something new. after he dings 70, i'm planning on doing a lot of BGs for honor so i can get some pvp gear, but i heard demo is more pve oriented whereas afflic and/or des is more pvp oriented. my question is if i respec but decide later to be demo again, will i have to rebuy all the books for my felguard or will they be remembered? i'd hate to know that i wasted my money and would have to rebuy them all over again