You can replace it with any model you wish. Your biggest concern is going to be the dimensions of the old cooktop and the new. If the new unit is smaller than the old, you're going to have a problem mounting it in the counter top.
As it is, plain stove tops normally mount in a hole in the counter top like the sink does, while stove/oven combos slide into the cabinet, requiring the counter top cutout to go all the way to the edge. What do you plan to do with the hole where the oven was?
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