I use 20 gauge fine silver wire for my half-drilled pearl projects. I
usually have half an inch or so extending from the piece after I set the
wire. I trim off the excess when I'm ready to set the pearl, but I find
having it longer during placement and finishing makes the process easer.

Depending on the design of the piece, I will put a tiny bend into the end of
the wire that is being inserted into the clay. Then, after it's been
pressed in, I can fill the extra gap it made with paste or syringe material.
This little hook prevents the wire from pulling out.

In some cases, such as at the tip of a small tapered coil, making the bend
is not a possibility. In those cases, I'm always extra careful reinforce
with paste around the base of the wire. For the wire in the end of the coil
I might even smooth clay along the wire to increase the hold and make the
transition between clay and wire smoother.

Instead of trying to put a tiny bend in the end of the wire, it might be more efficient and place better if you use a torch to ball up the end of the wire to be pushed into the clay. As before, you'd need to fill in around the wire where the larger end pushed back the clay.

In either case, once your piece is dry and ready to fire the wire should not
be loose at all. If it is, go back and reinforce again. Using these
techniques, I have had no problem with the wires pulling our or surviving
firing, tumbling or other finishing processes.

I set my pearls using two part epoxy. I use a slow curing formula (Loctite
Extra Time Epoxy) so I don't feel rushed while getting the pearl set. Avoid
super-glue or other cyanoacrylate glues as they can become brittle over
time. I trim the wire in stages. Trim it, put the pearl on the wire and
see how much more you need to trim. You can always take more off, but you
can't put more on after you cut it, so it's better to work you way down to
the correct length slowly. Once you have the wire trimmed to the correct
length, use a toothpick to mix up the epoxy and put a small drop on the end
of the wire. Push the pearl onto the wire, twisting it a bit to make sure
the epoxy is well distributed inside the hole.