Part of it doesnt make sense because what would future Barry merge with... his 10 yr old self? if thats the case barry wouldve been called crazy having all those future memories..
I agree Barry ceased to exist... but I dont know how yet.. Maybe he merged with Eobard and Barry's positive speed force cancelled out his negative speed force.
Or what if Saving his younger self changed the timeline then he ceased to exist... But then Eobard created a new timeline when he found Wells and created the particle accelelator earlier...
I wouldn't think a 10 year old mind would completely understand what just done happened, and when Barry at age 10 tried to explain it, people thought he was crazy. It's different from modern day Barry who was aware of who he is, and already had knowledge of the possibility of time travel and only going back a day. Those things are still fresh in his mind, but trying to do that as a 10 year old., I doubt it.