I will address these 2 separately.
If we assume a date of Fall 2025 for the restoration of the Northlander, I would expect that by 2030, we will know whether its return is a success. So, if the province wnts to get into intercity passenger rail in a large way, I would suspect by then something would be released, possibly near an election as a way to buy votes.
At the east end, the only other users would be the Totten mine and the lumber mill in Narin Centre. If this line were to be abandoned, I feel that the middle section would be gone. However, If the continued viability of the companies along the line becomes in question due to the closure of the line, that would be the reason for the ONR to own it.
Lets look at populations,
ONR North of North Bay, not including North Bay
Cochrane 5,321
Iroquois Falls 4,537
Timmins 41,145
Black River-Matheson 2,438
Kirkland Lake 7,981
Englehart 1,479
Earlton 1,166
Larder Lake 730
Temiskaming Shores 9,634
Cobalt 1,128
Temagami 802
Total: 76,356
HCR,not including Sudbury, but including SSM:
Sault Ste. Marie 72,051
Blind River 3,472
Sables-Spanish Rivers 3,214
Elliot Lake 11,372
Espanola 4,996
Total: 95,104
en.wikipedia.org
So, to argue that there isn't the population base for supporting it on the HCR vs the ONR isn't true.
These next few years will be interesting for the HCR line. It may show what the province is willing to do.