Does a black hole dissipate when there is nothing left to devour  ?

No they do not as a matter of fact they may be the reasons for our little part of the universe since they are part of a cyclic system...

From the great suck to the big bang over and over again but it take trillions of years to do that...

N.Shadows

no they swallow up planets and then they explode from the materials that have built up , an normal thing to happen , same as how the universe happened , endless process , like the process  from the sun , it works on a 2 gas system , one process a gas , while the other rots to form the  other gas ,

There is no place for racism on this site.

No, the mass is still there.  Why would it dissipate?

Nothing left to devour means not a single molecule left, then yes, Hawking radiation depletes a minuscule amount of mass over eons of time.

A stellar size black hole has a lifetime of about 10^68 years. The universe is only about 10^10 years old. That means every black hole that was ever formed after the Big Bang will last at least another 10^58 years before they evaporate through Hawking radiation. There is still the possibility of primordial blacks created at the Big Bang that might have been smaller and with shorter life spans, but none have been detected.

Basic thermodynamics shows that a totally isolated black hole at our current time will still gain mass/energy since it is colder than the CMBR that permeates the universe. A stellar black hole has a temperature about a 100 million times colder than the 2.7 degree K CMBR.

A black hole doesn't dissipate, but it does lose mass by Hawking radiation. After a very long time, it will be gone completely. 

Space bacteria consumes it.

does that make any sense to you...no..its just that when its not eating anything we cannot see it

Well... sorta. It's thought that Hawking radiation is emitted from black holes, removing a bit of it's mass; the smaller the mass, the more rapidly they 'evaporate'...  

With nothing to feed on, the black hole would supposedly get smaller and smaller.