Before Voyager's second season aired, there were rumors Decker would appear in "The '37s" as one of the displaced humans encountered by Janeway and her crew.
IIRC, the Decker return was for a different
episode. The writers were thinking that TMP's Voyager 6 might have a destiny with USS Voyager
. But Stephen Collins was still contracted to "Seventh Heaven", IIRC, and around the same time Persis Khambatta passed away. The concept for an episode focusing on Will Decker never went any further.
As for the Ilia Probe, the novelization of TMP tells us that the probe that invades the bridge is essentially the same probe
that impersonates Ilia.
When the script was "In Thy Image", Chekov christens the first probe "Tasha", due to its pearlescent appearance, reminding him of his Aunt Tasha's pearl ring. At the end of the telemovie, Ilia is miraculously restored, and they find the charred "light bee" device (that had generated its Ilia guise) lying on the ground.