leave without completing study

I have one more year remaining to finish my study. But I want to return my country after leaving school right now. Knowing this, how college terminates my visa? How long can I stay Japan after termination from college? Can I work during these periods before leaving Japan?

No, the college cannot "terminate your visa", only the immigration bureau can. If and when they do, you'll hear about it.

Oh, and about whether you can work after you have left school, typically no, but you need to consult the text of your "work permit" to be sure.

when you leave school, you will lose the work permission (28 hr/week) and your student status.
you have to leave Japan.
when you leave school, the school report your leave to immigration within 2 weeks.
they may wait for a few month (probably) until you find a new school. (as similar as working status).
it is a bad idea that you continue to work, because you have to show your "my number" to the employer, when you work. they will know you are working. and, of course, you could be an over-stayer.
also, if you work more than 28 hr/week, they may know the overwork.
when you apply a working visa after graduation, they might not give a working visa (status) because of that reason.
employers report your "my number" from this year (from last year payments) to tax office. they are collecting those data. you have to be careful. don't underestimate their works.

Once you stop studying at the school, the school will report that you left, and you will report that you left, within two weeks, to the authorities. Your school cannot terminate your resident status (visa, as you call it).

If you want to stay around in Japan to travel a bit, immigration might suggest you change it to Temporary Visitor status, but if you are simply leaving Japan, or planning to find another school soon, probably they would not say anything.

Now that you are leaving the school, it is not like you are on school holidays, so I would say it is a bad idea to work, but as Firas says, check the work permit.

your work permission is valid, when you are a student, not because of having a student visa (status).

Generally, student visa holders have an obligation to notify the Immigration Office within 14 days after leaving the study. The Immigration Office has the right to cancel a student visa.

Generally, you canft keep your student visa until it expires if youfre not studying, or as Immigration puts it, not gengaging in authorized activities.h Ultimately, however, Immigration will make decisions on a case-by-case basis.

As long if you have a student visa you may work 28H a week. But in your case I don`t know if that is smart to do.

Anyway always consult the immigration office and they can inform you the best. They are also humans and and they will guide you well.