Then I read your comment (thank you very much) and explored "Show graphics" command and beyond at BOINC Manager.
When selecting a running Theory task, command "Show graphics" gets enabled.
When pressing "Show graphics", an explorer window opens, containing a link to "logs".
If that link is pressed, a very useful "Index of /logs/" page opens.
That page contains a "Last Modified:" label that gives a clue on whether "running.log" file has been recently updated or not.
When updating "running.log" file becomes frozen, it can be taken as a warning to abort the corresponding task.
And if "running.log" is being periodically updated, it can be taken as a signal that the task is still alive.
"Index of /logs/" page also contains a link to "running.log" file itself.
At the beginning of "running.log" file, a definition of the task is shown.
The penultimate parameter on the first line indicates the stated number of events for the task. 55000 in this example.
And at the end of the file, progress of the task can be followed.

Wow, many thanks for the detailed explanation! Can't wait to get home tomorrow and check my two long tasks.

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Thanks for all that step-by-step info!

Is running.log an actual file on disk? If so, do you (or anyone) know where it is on a Win10 machine?

Thanks.

Is running.log an actual file on disk?

No, it isn't. It's located on a VirtualBox virtual machine, on one of the Linux OS partitions. However, VirtualBox forwards a link to this file to Windows 10 as http://localhost:port/logs/running.log , where port is a number, such as 6079. Each user will have their own ports open.

Unfortunately someone broke your record during the last 100 tasks:

Theory Simulation 4930 6784 3.52 (0.03 - 489.41)
20 days - 9 hours - 25 minutes

I use to have such long tasks once in while :-)

Wow!
One task like that, must have started on past year !-)

Wow!
One task like that, must have started on past year !-)

I just killed such one, after 21 days, having noticed (obviously much too late) that it somehow got stuck.

Thanks for all that step-by-step info!

Is running.log an actual file on disk? If so, do you (or anyone) know where it is on a Win10 machine?

As long as the task keeps running and stay in memory the running.log from the VM is stored on the host-disk with a different name.
Default location: C:\ProgramData\BOINC\slots\slotnumber\shared\runRivet.log

When task duration exceeds certain limits, it is easy to get lost among thousands of seconds...
I made a simple spreadsheet for my own clarification.
It looks as follows: