Let's do a small experiment:

root# dpkg -i dummy_1_all.deb
Selecting previously deselected package dummy.
(Reading database ... 288646 files and directories currently installed.)
Unpacking dummy (from dummy_1_all.deb) ...
Setting up dummy (1) ...
# No postinst, no preinst, nothing
root# cat /var/lib/dpkg/info/dummy.conffiles
/etc/dummy/test1
root# ls -l /etc/dummy/test1
-rw-r--r-- 1 root root 9 Mar 18 01:01 /etc/dummy/test1
root# cat /etc/dummy/test1
coshoopu
root# echo "I am a bug" > /tmp/a
root# rm /etc/dummy/test1; ln -s /tmp/a /etc/dummy/test1; cat /etc/dummy/test1
I am a bug
root# ls -l /etc/dummy/test1
lrwxrwxrwx 1 root root 6 Mar 19 22:19 /etc/dummy/test1 -> /tmp/a
root# dpkg -i dummy_3_all.deb # new conffile
(Reading database ... 288653 files and directories currently installed.)
Preparing to replace dummy 1 (using dummy_3_all.deb) ...
Unpacking replacement dummy ...
Setting up dummy (3) ...
root# ls -l /etc/dummy/
total 4
lrwxrwxrwx 1 root root 6 Mar 19 22:19 test1 -> /tmp/a
-rw-r--r-- 1 root root 9 Mar 18 01:15 test1.dpkg-new


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#===================> No prompt !
#Nothing said about anything changed.
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