Underlying contributory esa

I’m just about to do my managed migration to uc, and Im a little confused by something, and wonder if you could help. I spoke to citizens advice helpline, and although they were very helpful, I couldn’t get a clear answer on this point.
I have a claim for esa ( and its predecessor) going back to 2002. At that time I had a long work history and was entitled to the Non means tested version, indeed that’s all I claimed as I had a high ish level of savings. When I migrated to esa in 2015, the breakdown continued to show contributory benefit topped up by income related ( as I now had little savings), which because I qualified for the various ad ons, like severe disability premium etc, added about another £100 to my weekly benefit in income related benefit.
This continued. However in my last breakdown, it just shows my entitlement as one figure, presumably of the income related benefit, even though nothing has actually changed in my circumstances.
So what I’m trying to find out is that now I’m migrating to UC, will I have a separate new style entitlement, and then a uc payment topup, or will it be all as uc ? The reason I ask is that should I be lucky enough to get a windfall in the future that takes me over the savings limit, it would allow me to still get a partial benefit in the future ? ( ie new style)
I’ve tried to do some research on this before writing in, but I’m not fully understanding, how long the qualification for contributory lasts, if it’s a continuous claim? Or has the law changed ?
Be most grateful for an explanation. Thank you.