In general, I think Buffy gives good advise.
Update since OP clarified that this was not a formal procedure, and not even a group seminar, but a meeting with two supervisors which ended up becoming a meeting with one supervisor.
IMHO it is still impolite of the supervisor to not show up without notifying you, after all, it was a scheduled meeting with you. I expect there's a good excuse, and/or maybe an explanation of what went wrong (e.g. co-supervisor thought you knew already).
There's no need here to worry about the supervisor's wellbeing or at least not more than in general if someone is missing some meeting with you.
Since you seem to worry more:
On a personal level, your supervisor may consider this anywhere between nice and intrusive.
Which, we cannot decide here on the internet.
But: people are different, you recognizing that you'd want someone to be worried about you works as a 0th approximation, but already in 1st approximation you need to consider that this is not always everyone's wish. They may (quite likely, the more so since you are neither family nor friends) be in a situation where the right thing for you to do is not to bother them additionally.
Side note: since we are strangers on the internet, I can only know that people exist who worry too much (some even have anxiety disorders). I'd think it more likely (bachelor thesis presentation) you are new to this situation and ask here because this is a new situation for you, and you are therefore uncertain. Thus:
Professionally speaking, the situation is clear: their absence is none of your business.
They have to notify their employer (i.e. university) about their absence, but not their students. Others (administration, co-supervisor) thus should typically not tell you anything about their absence at all, and much less about the reasons. I.e., except as much as concerned you wrt. the meeting.
I don't see anything in your description of the situation that would suggest something so far out of the ordinary in terms of danger to the supervisor that you should disregard these professional considerations.
old answer
To me, there are 2 aspects here:
If this was a formal thesis defense, there's a slight aspect of your supervisor having left you in the lurch. I.e., a "Prof. X asks you to excuse their absence from your defense due to unforeseen circumstances." would have been indicated.
Since that apparently did not happen, I'd recommend that you for yourself excuse this and otherwise forget it.
There's the aspect of you being worried about the wellbeing of your supervisor.
On a personal level, that may be considered (by them) anywhere between nice and intrusive. Professionally speaking, their absence is none of your business under the given circumstances:
In this particular case, the burden of notifying someone if that is necessary is on the co-supervisor (or possibly the chair of the meeting), not on you.
If that presentation was part of the formal thesis procedure:
I find it highly unusual that you weren't notified, since that can put you under stress and negatively affect your presentation performance.
But I think it quite possible that this was forgotten in the hectic e.g. because the co-supervisor was under the (wrong) impression that your supervisor (or someone from the exam office) had notified you already.
it will already on record that your supervisor did not attend. Thus, not only your co-supervisor but also administration will already be aware of your supervisor's absence. Absence from exam duties tends to be something that needs immediate explanations.
If the presentation is not part of the formal thesis procedure but just a seminar-type group-internal presentation of your work
The absence of your supervisor does not need more explanation than the absence of a supervisor at any group seminar. I have worked in a group where that happened regularly and was announced by whoever took over the chairing of the seminar by "Prof. X won't come today, let's start."
Whoever took over the chairing of the presentation (co-supervisor?) will naturally have decided (possibly together with your supervisor, but unknown to you) that it is better to have the presentation even if your supervisor misses it than to postpone the presentation.
Again, this is something that doesn't just happen without being aware that your supervisor is absent.
Still, it would have been nicer to clearly communicate this with you.
So, there is no need for you to worry - others who are higher up in the department/closer to administration are aware.
Still, if you are worried, you can bring up your concerns e.g. to the co-supervisor or the chair of the presentation.
