There remains to be done *much* discovering of fossils before anything is certain, at the very least.
There is an underlying confusion here. The nature of fossils (just bones) is such that having
all of them wouldn't make the theory 'certain'.
The theory is "how" -- that is by what mechanisms life developed over time. If by "certain" you mean we know each mutation and selection event then of course it will never be certain. The bones won't show that.
However, there are way more than enough bones to be as close as we can get to "certain" that evolution (not the mechanism but the fact that life
has changed ) has happened (by whatever mechanism). Philosophically science is supposed to remain open to change by continuous checking. However, that life has evolved (by some means) is, in any reasonable sense, absolutely certain.
Meanwhile the theory of evolution (what that mechanism was ) is the only viable contender for an explanation that we have.
We are way beyond fossils in our checking and developing of our understanding of that. While fossils would be helpful in showing the details of the actual steps taken they would not, I think, help with understanding the details of the theory at all.
What we need now is an understanding of gene expression, genotype changes and biochemical pathways.
The theory says mutations supply the raw material and that selection drives the process in non random ways. We have a lot of understanding of how that works at a high level.
What we will learn in the future is exactly how gene changes can arise (not just "mutation") and how particular ones may be expressed and selected. That is there the theory will be strengthened.