Yes, there are many, many unique organisms that lived, that are preserved but that geologists have simply not found.

Discoveries are made EVERYDAY of new fossil forms as well as nicely preserved versions of fossils we already have, but are of limited use because of poor preservation.

Her is an interesting link that you will love

There are more fossils that haven’t been found than have been found. There are lots of rocks under the surface of the Earth that will at some time be brought to the surface and expose new fossils.

Yes, lots - paleontologists are continually finding fossils of animals, plants, and sometimes microbes that nobody has ever known about before.

Absolutely! Not only are there plenty of fossils yet to be found (way more than have already been found, in fact), many fossils representing new species have yet to be found as well. A good analogy would be gold or oil; a lot of both of these substances is still in the ground waiting to be discovered.

With almost absolute certainty!

In science it's impossible to prove something absolutely. In this case, the only way to prove there are no more fossils is to excavate every square inch of dirt, and then you'd have to make sure you didn't destroy any of the fossils. Also, even bacteria (which are often too small to see with the human eye) can be fossilized, so they would be easy to miss! So, although it's impossible to prove that there are more fossils that haven't been found, it is extremely unlikely that we have found them all. As time goes on, we find new fossils, and this is evidence that we should continue.