Is it reasonable to expect a company to survive 100s of years? Not really
Is it reasonable to expect a TRUST to survive 100s of years? Sure
The character in question had a trust set up. This is made clear by the dialog, as he is tying to find his trustee. Barring fraud by the trustee, or overspending by the benefactor, well capitalized trusts will last basically forever unless you have truly massive economic upheavals and/or government seizure of assets)
In fact, it such a issue, that English Common law there is a " rule against perpetuities" that limits the lifespan of non-charitable trusts as it thought of as unwise to allow dead men or women control capital 100s of years after their death. Historically it was 21 years after the death of the last living person named in the trust, (with some modification of persons in the womb). However in many juristictions they have gone with a 90 year rule (trusts need to be liquidated in 90 years) or extending them. For example, Florida seeking trust business allows 360 years. A classic example is many trusts where set up of native land in hawaii, and in the last few years the non-charitable trusts have started to hit this limit, causing farmland to be sold that has not been open for sale in 100+ years.
as a note, the "living persons" can be anyone who is traceable. so for example, you could set up a trust saying 21 years after the last current living decedent of queen Victoria dies and that will be upheld.
So if the person set up a trust that included land and other diverse assets, and in a area without the rule against perpetuities, it quite reasonable to assume that there would be some sort of asset in the trust in 200 years.