its next to impossible to brick an s-on,
unlocked device with software flashes of system or boot,htcdev unlock is extremely safe since it is protecting the bootloader and radios.
when you have trouble,you should always be able to relock and run an ruu.
you can re-unlock with your original token,and try again. as was said,this time make a backup
if youre on software 2.20.502.7,make sure you understand how to flash the boot image seperately,as the newest hboot is preventing recovery from installing the kernel. you also should try to launch your recovery into memory,rather than booting to is with the command:
fastboot boot recoveryname.img on other devices,this lets the kernel flash,just like an s-off device,defiantely simplifying the install process
not sure why you were having trouble installing twrp... thats the recovery i run on mine,not being fan of clockwork. did you have the image inside the same folder with adb/fastboot? it wasn an .img file correct,not a .zip or .nbh,or some other type of file?
technically,you can install things a PxxxIMG files,but i personally avoid that when s-on
unlocked,as the phone is still doing checks and the android info text document info comes into play,and makes it a PITA
just holler if you have any questions