Are internet brokers selling actual shares in company or some kind of derivatives?

When you buy shares on a US stock broker's platform, your shares will usually be held in street name. In street name registration, you are the beneficial owner, but the shares are held in the stock brokerage's name (i.e. your name will not appear in the company's share register). This is for convenience.

You may want to read this SEC article to learn more about the way your shares are held: Holding Your Securities - Get the Facts.

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For example if Interactive Brokers suddenly disappears (goes bankrupt or wiped off the face of Earth for any other reason) will my shares disappear with it?

You should be protected by the Securities Investor Protection Corporation (SIPC). The SEC article I provided above mentions this too. Relevant excerpt:

Q: How are my securities protected if I choose street name ownership?

A: Nearly all broker-dealers are members of Securities Investor Protection Corporation ("SIPC"). As a result your securities and money held at your broker-dealer are protected up to $500,000 with a $100,000 limit for cash. Many broker-dealers also carry insurance in excess of SIPC's coverage. However, SIPC does not protect you against losses caused by a decline in the market value of your securities. For more information about SIPC coverage, please read our "Fast Answer" on the Securities Investors Protection Corporation.

Further information from FINRA: Your Rights Under SIPC Protection.