Should this sentence have a possessive apostrophe at the end of it?
Unfortunately, the list below is similar to the original vendors.
Should this sentence have a possessive apostrophe at the end of it?
Unfortunately, the list below is similar to the original vendors.
Whether the noun-phrase (NP) ends a sentence is totally irrelevant. The same rules apply in any position. So:
The list is similar to the vendors.
= The list is similar to the vendors (the vendors are similar to the list!) -- probably not what you mean.
The list is similar to the vendors'.
= The list is similar to the vendors' one (the list of the vendors), evidently what you want to say.
Yes, if this is possessive, it should have an apostrophe after the last S:
Unfortunately, the list below is similar to the original vendors'.
If it is not possessive and the vendors are being compared to the list, it would stay the same as you put it in the question:
Unfortunately, the list below is similar to the original vendors.
Another way that you can articulate that you are referring to the lists is by putting "lists" later in the passage:
Unfortunately, the [one] below is similar to the original vendors' lists.
I hope this helps!