Thanks all for your feedback. Truly appreciate it. One less thing for me to worry about.. as my ex would be equally responsible.
If you look at the document you signed, this is all tremendously clear and written in plain English (at least I think so).
"I understand the undertaking remains in effect no matter what may change in my life. For example,
if I am divorced ... I will still be responsible to the sponsored person and his or her family members...".
"I understand that I will be in default if a government makes a payment that I have promised to pay in this undertaking. ...
all social assistance paid to the sponsored person ... becomes a debt owed by me to [the Crown/the government of Canada/the relevant province.]"
"As a result, the Minister and the province concerned
have a right to take enforcement action against me (as sponsor or co-signer) alone, or against both of us."
You should not feel that there is one less thing to worry about; you and your spouse are responsible together or separately, for the full amounts, subject only to the language above (meaning amounts paid). This means that if the government decides to go after you - instead of your spouse, or at same time as your spouse, whatever - they can. It's your problem (despite the fact that you've divorced). You can sue your spouse later if you want, that's your problem (and I have no idea whether or not your ex-spouse would be required to 'share' the amounts paid - again, that's your problem, and costs and difficulty of getting the funds from your former spouse are ... yep, your problem).
The timeframe is also clearly disclosed - so should be no surprise.
[Background: full credit to government for using plain language in this undertaking - but it's clearly a restatement of the common law concept of "joint and several", meaning you're both on the hook, and the other side (government in this case) can go after whomever it chooses to recover what it thinks is owing, and it's up to those on the pointed end of the pétard to "sort it out" amongst themselves.]
On the bright side (from your perspective) - it does seem that the sponsor/co-signers are not expected to cover "public health" expenditures. I don't know how that applies in specific case of citizens who may not yet be covered by provincial health plans, but at least
somewhat limited. (Limited at least in terms of time and most likely scope (dollars) as there are mostly no pre-existing condition type issues under public health care - so practically you probably won't be on the hook for the proverbial six million dollar [wo-]man.)
In other words, I
think your liability will mostly be limited to what's listed in the document you signed: food, clothing, shelter, fuel, utilities, household supplies [etc] ... and other goods and services,
including dental care, eye care, and other health care needs not provided by public health care."
And for the most part, these won't come up unless your MiL somehow gets government to pay for them.
But to reiterate: there's really no mystery in the spnsorship document you signed, it's there in plain English.