Depends on whether they're 'fully cooked' sausaged which you reheat or raw. If they lack expiration dates and are vacuum sealed and are the already cooked kind, they're probably safe as long as they don't smell off when you open the package.

In particular, the sweet chinese sausages, if they're cooked, last months and months, possibly even up to a year. No, really.

And in terms of preservatives, it's mostly sugar and salt. (So many people forget that sugar and salt are preservatives. I continue to laugh at the comercials talking about 'Jam with no preservatives'.)