bas rutten used downward elbow strikes in the ufc bas-randleman fight. to this day he has bone splinters in his elbow and it's huge and painful and commonly gives him problems and even gets infected from time to time.
smashing your hard bone into someone else's hard bone is not wise. the forehead/skull is very solid which is why it can break your hand and we use gloves. you should use your palm which is softer and padded. palm strike his forehead if you must to soften him up and give him the headache. it's less damaging but the damage you'll take is 0. you can toe-kick someone and hurt them but if you break your toes then what good is it for you?
i didnt invent the triangle-kimura but it's my go-to when the triangle isn't getting the job done. you alwways need a good plan B and i feel this is flashy. if im triangling someone good, they know not to panic and give me the armbar and the omoplata is hard on a lot of decent guys so i basically omoplata with my free arms--the kimura.
if i can tell the triangle isn't choking him (IE his head isn't red, he's not flopping over or losing posture) then his shoulder is probably a little to deep into my legs. this means i didn't stretch him out, but i managed to lock my legs for the triangle anyways--i did a crap triangle. it leaves me in a good position and it's still hard for him to escape unless i just give it up. so i just keep the good position and sub from there. if he's locking his hands around your hip that's perfect. just bridge up and get your butt off the mat, then grab his wrist and lock your arm out. drop your bridged hips down and your locked arm will peel his wrist off your hip. sit up and kimura. keep your triangle on because there's no reason to let it go and the tap is easy.
if you cant manage to peel him off even if you try a few times because he's crazy strong or if he pulls his arm away before you can post/lock then you can just elbow roll by grabbing his elbow, posting your free arm behind you and thrusting your hips like you're in guard trying to do the same move.