Is the retainer plate necessary to have?

If you are sure the suspension you have uses the bearing retainer style of spindle and it's not there then, no it is not safe to drive it as the plate is what holds the bearing in place. However they used 2 different front spindles on the Neons, one uses the plate with bolts while the other uses an internal snap ring in the bearing bore. Yours would have come with the retainer plate version but they can be swapped around.
Why do you think yours is missing? Could you perhaps take a picture of the missing area just to be sure we are talking about the same part. The bearing retainer I'm referring to is in the attached image.

It was the plate but I found two of the three bolts that hold the plate on or broke off into the knuckle or spindle and then there was only one left on there. so I wouldn't put that one back on because I had to drive to the parts store to get the the screws and we were going to you know knock them out of the the holes of the spindle the ones that broke off in there, but when we got back and we went to go get into it the whole entire plate was missing. I think it probably fell off while I was driving. but my next question was going to be can I can I swap the snap ring can I use the snap ring or the retainer ring instead of the retainer for for this? Because I have a ring, I mean I asked when I bought I forgot what I bought this like my third set of of bearings I had to redo so when I bought that I bought the ring instead of the plate which I wasn't thinking clearly but I have the ring for it so it is okay to use the ring instead of the the plate need be.

Oh and yes definitely the same part my car is at another location right now.

You could use the ring but the hub needs to have the groove inside it for the ring to seat into and if you have the retainer plate it doesn't have the groove. The reason being is that the bearing in the plate version sets just about flush on the knuckle while the snap ring style sets into the knuckle about a quarter inch with the snap ring groove just in front of the bearing. Unless the retainer was rusted through it shouldn't come off as it circles the hub assembly, so if yours is gone, it needed replacement.