How companies are accepting bitcoin for their products or services?
Many companies will instantly convert bitcoins to fiat upon receiving. This is done by the payment gateways themselves like Bitpay, coinify.

However, these days you see several website keeping the bitcoins without converting them. You can use payment gateways like blockonomics, blockchain.info, coinsimple etc. This is due to several reasons:


Extra fee in converting
Regulations/KYC in accepting fiat
Bitcoins are scarce  
Adoption has increased. Employees are taking wages in BTC, and business can buy stuff like airline tickets and other required goods directly using bitcoins


If you hold bitcoins over a long enough period (say 1year+) you will see that the value has always increased https://www.reddit.com/r/Bitcoin/comments/5vuox8/i_dont_mean_to_brag_but_i_bought_bitcoin_at_the/