to re-activate the links AFIK you've got to recheck Smart Links in the menu, and then go to each one, double-click to edit the cell content, and type a space at the end.
It turns out that it is possible to activate/reactive links without going through each one manually! Numbers uses a format called rtf (rich text format) to copy-paste cell information, including links, between cells. So it is possible to have a script copy a cell's contents to the clipboard, convert that to html, extract just the link part from the html, form the html for a complete link (if necessary), convert the html to rtf, and paste the rtf back into the cell.
So several active and inactive links like these:

Can quickly be batch converted into live links like these:

- Copy-paste the script below into Script Editor (in Applications > Utilities)
- Select the cells with the links, here A2:A6
- Click the triangle 'run' button.
As always make a backup first, as this script will change the content of the selected cells.
SG
-- reactivates "dead" links or activates "link html" in Numbers cells
-- select the cells with links and run
tell application "Numbers"
activate -- puts focus on app for GUI scripting
tell front document's active sheet
tell (first table whose selection range's class is range)
set selRng to selection range
repeat with c in selRng's cells
set selection range to c
delay 0.1
-- copy to clipboard and set clipboard to the RTF class
tell application "System Events" to keystroke "c" using command down
set the clipboard to (the clipboard as «class RTF »)
-- convert clipboard contents to html using textutil
set theHTML to do shell script "pbpaste -Prefer rtf | textutil -convert html -stdin -stdout"
-- extract the contents between <span and /span>
set spanText to my extractSpanText(theHTML)
if spanText contains "href=" then -- decode any "html entities" (&-encoded)
set htmlLink to do shell script "echo " & quoted form of spanText & ¬
" | php -r \"print html_entity_decode(file_get_contents('php://stdin'));\""
else -- construct complete link in form: <a href="http://www.apple.com/">Apple</a>
set htmlLink to "<a href=\"http://" & spanText & quote & ">" & spanText & "</a>"
end if
-- convert link html to rtf and copy to clipboard
do shell script "echo " & htmlLink's quoted form & ¬
" | textutil -format html -encoding UTF-8 -convert rtf -stdin -stdout | pbcopy"
-- paste the rtf into the Numbers cell -- live again!
tell application "System Events" to keystroke "v" using command down
end repeat
end tell
end tell
end tell
to extractSpanText(theHTML)
set text item delimiters to {"<span class=\"s1\">", "</span>"}
theHTML's text item 2
end extractSpanText