Уважение к нему и сейчас в стране существует, и немалое.
or
Уважение к нему и сейчас в стране существует, и не малое.
Уважение к нему и сейчас в стране существует, и немалое.
or
Уважение к нему и сейчас в стране существует, и не малое.
Unfortunately, “не” with adjectives and participles is quite tricky in Russian. So, even large part of native speakers cannot write it properly very often.
Basically you write “не” seprately if:
For example:
Уважение к нему и сейчас в стране существует, и совсем не малое.
Уважение к нему и сейчас в стране существует, и не малое, а довольно значительное.
In your “short” case you most likely shoud use “немалое”.
In common usage one can apply the rule of thumb as follows:
If you can replace “не”-something in sentence with a one-word synonym (not containing “не” prefix) without losing any meaning and context, you should write it as one word.
Уважение к нему и сейчас в стране существует, и значительное.
More information about “не” you can find in grammar rules (in Russian):
https://therules.ru/hyphen-particles/#88
(§ 88 and so on)
In addition to what has been said, one trick for deciding how to write не with an adjective -- слитно or раздельно -- is by examining whether не together with its adjective assert/affirm a property of the noun phrase, in which case you should write them слитно, or reject/deny it (i.e. property), in which case it is раздельно.
Telling the difference between the two can be sometimes quite tricky, but in your example it's quite obvious that немалое should be chosen -- you are clearly asserting that this man is of notable repute rather than trying to dismiss the claim that there's little respect for him.
To show how не малое can pop up in a setting similar to the one you provide, imagine a dialogue:
Person А: Уважение к нему сейчас в стране малое.
Person В: Неправда, не малое...
The word малое can be said to be out of place in this particular Person A's phrase and in need of being changed for, say, маленькое, but style is not the important thing here. The important thing is that не and малое are written раздельно in Person B's response -- for the very reason that Person B is not asserting that the man is held in high respect, but denying that respect for him is low.