These are really two separate questions with two separate answers.
For the first question, code G8730 only needs to be reported when you are participating in MIPS — a CMS Quality Payment Program — and yes they are active. While many chiropractic physicians are not mandated to participate in MIPS due to the low volume threshold, you may choose to participate by either voluntarily reporting (which has no payment offsets) or opting in. Beginning in 2019, providers can opt into the MIPS program and be eligible for MIPS payment adjustments in the 2021 payment year.
For the second question, it is essential to note that there are many other G codes that are still active and required for non-quality reporting (e.g., G0283 for electrical stimulation). In fact, new G codes are added each year to the HCPCS code set. Be sure to use the appropriate procedural G codes as required by payers.